LABORATORY  MANUAL 

OF 

GLASS-BLOWING 


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LABORATORY  MANUAL 


OF 


GLASS-BLOWING 


BY 
FRANCIS  C.  FRARY,  PH.  D. 

ASSISTANT   PROFESSOR    OF    CHEMISTRY 
UNIVERSITY    OF    MINNESOTA 


McGRAW-HILL  BOOK  COMPANY,  INC. 
239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE  STREET,   LONDON,  E.  C. 

1914 


COPYRIGHT,  1914,  BY  THE 
MCGRAW-HILL  BOOK  COMPANY,  INC. 


PREFACE 

The  purpose  of  this  little  book  is  to  provide  a  clear  and 
detailed  discussion  of  the  elements  of  glass-blowing. 
Many  laboratories  in  this  country,  especially  in  the  west, 
are  located  a  long  way  from  any  professional  glass-blower, 
and  the  time  and  money  spent  in  shipping  broken  appa- 
ratus several  hundred  miles  to  be  mended  could  often 
be  saved  if  some  of  the  laboratory  force  could  seal  on  a 
new  stop-cock,  replace  a  broken  tube,  or  make  some 
temporary  repairs.  Many  men  in  physical  or  chemical 
laboratories  have  occasion  to  modify  some  piece  of  appa- 
ratus designed  perhaps  for  other  uses,  or  to  design  new 
apparatus.  To  such  also,  the  ability  to  perform  some  of 
the  operations  herein  described  may  be  very  valuable. 

No  originality  is  claimed  for  the  methods  here  de- 
scribed. They  are  those  which  the  author  has  found 
most  suitable  and  convenient  in  his  own  work,  and  most 
easily  learned  by  students.  The  aim  has  been  to  describe 
each  operation  in  such  detail  that  a  beginner  can  follow 
the  process  without  help  and,  with  practice,  attain 
satisfactory  results.  It  is,  however,  much  easier  to  per- 
form any  of  the  operations  described,  after  seeing  some 
one  else  perform  it  correctly;  since  the  temperature,  the 
exact  time  to  begin  blowing  the  glass,  and  many  other  little 
details  are  very  difficult  to  obtain  from  a  description. 

It  has  not  been  thought  worth  while  to  describe  the 
process  of  making  stop-cocks,  thermometers,  vacuum 
tubes,  etc.,  as  such  things  can  be  purchased  more  cheaply 
and  of  much  better  quality  than  any  amateur  can  make 
unless  he  is  willing  to  spend  a  very  large  amount  of  time 
,  in  practice.  For  similar  reasons  the  manipulation  of 
quartz  glass  has  been  omitted. 


"vi  PREFACE 

The  author  will  be  grateful  for  all  suggestions  and  crit- 
icisms tending  to  improve  the  methods  presented  If 
some  of  them  appear  to  be  given  in  excessive  detail,  the 
reader  will  remember  that  many  things  which  are  obvious 
to  the  experienced  worker  are  not  so  to  the  beginner,  and 
that  it  is  the  little  details  in  the  manipulation  which 
often  spell  success  or  failure  in  glass-blowing. 

F.  C.  F. 

MINNEAPOLIS,  MINN., 
January,   1914. 


CONTENTS 


PAGE 

PREFACE   v 

CHAPTER  I 

MATERIALS  AND  APPARATUS 1 

Varieties  and  defects  of  glass — Devitrification — Anneal- 
ing glass — Blowpipe  and  bellows — Light — Arrangement 
of  exercises. 

CHAPTER  II 

GENERAL  OPERATIONS 7 

Cutting,  bending,  constricting  and  flanging  the  tubing — 
Methods  of  rotation  and  blowing. 

CHAPTER  III 

ELEMENTARY  EXERCISES 16 

Joining  two  pieces  of  tubing  of  the  same  diameter — The 
"tee"  tube — Joining  two  tubes  of  different  diameters — 
Blowing  bulbs. 

CHAPTER  IV 

ADVANCED  EXERCISES 35 

Sealing  a  tube  through  another  tube:  The  gas- washing 
tube,  suction  pump,  and  Kjeldahl  trap. 

CHAPTER  V 

MODIFIED  METHODS  AND  SPECIAL  OPERATIONS 43 

Capillary  tubing — Glass  rod — Mending  stopcocks — 
Closed  circuits  of  tubing — Spirals — Ground  joints — 
Sealing  in  platinum  wire — Sealing  vacuum  tubes — Closed 
tubes  for  heating  under  pressure. 

INDEX 59 

v\\ 


LABORATORY 
MANUAL  OF  GLASS-BLOWING 

CHAPTER  I 
MATERIALS  AND  APPARATUS 

One  of  the  most  important  factors  in  the  success  of  any 
piece  of  glass-blowing  is  the  glass  employed.  As  is  well 
known,  there  are  two  general  varieties  of  glass:  Lead 
glass  and  soda  glass.  Formerly  much  apparatus  was 
made  of  lead  glass,  but  at  present  it  is  very  seldom  met 
with,  except  in  the  little  drops  of  special  glass  used  to  seal 
platinum  wires  into  the  larger  sizes  of  tubes.  Lead  glass 
is  softer  and  more  readily  fusible  than  soda  glass,  but  has 
the  disagreeable  property  of  growing  black  in  a  few 
seconds  unless  worked  in  a  strong  oxidizing  flame.  This 
may  be  prevented  by  using  a  "hissing"  flame,  with  a  large 
excess  of  air,  and  working  in  the  extreme  end  of  the  flame; 
or  the  black  lead  formed  may  thus  be  reoxidized,  and  the 
glass  restored  to  its  original  clearness. 

Almost  all  the  soft  glass  on  the  market  is  a  soda  glass, 
although  sometimes  part  of  the  soda  is  replaced  by 
potash.  Most  of  the  hard  glass  appears  to  be  a  potash 
glass.  The  following  qualities  are  desirable  in  a  glass  for 
ordinary  working:  (1)  moderately  low  working  tem- 
perature, (2)  freedom  from  air  bubbles,  striations  and 
irregularities,  (3)  proper  composition,  so  that  the  glass 
will  not  devitrify  or  crystallize  while  being  handled  at  its 
working  -temperature,  (4)  ability  to  withstand  rapid 
heating  without  cracking. 

The  working  temperature  of  different  samples  of  so- 

1 


,2         LABORATORY  MANUAL  OF  GLASS-BLOWING 

called  "soft  glass17  varies  a  good  deal,  and  is  best  deter- 
mined by  trial.  The  glass  should  become  almost  soft 
enough  for  blowing  in  a  flame  that  still  shows  a  little 
yellow  near  the  tip,  so  that  at  the  highest  temperature  of 
the  flame  it  may  flow  fairly  freely  and  thus  easily  elimi- 
nate irregularities  in  thickness.  If  the  glass  is  too  hard, 
the  shrinking  *of  the  glass,  collection  of  material  for  a 
bulb,  and  in  fact  most  of  the  working  processes  will  be 
slower,  and  the  glass  will  not  stay  at  its  Working  tem- 
perature long  enough  after  its  removal  from  the  flame 
to  permit  it  to  be  properly  blown. 

Air  bubbles  in  the  original  batch  of  glass  are  drawn  out 
into  long  hair-like  tubes  during  the  process  of  manufac- 
ture. When  such  tubing  is  worked,  the  walls  of  these 
microscopic  tubes  collapse  in  spots,  and  the  air  thus 
enclosed  will  often  collect  as  a  small  bubble  in  the  wall, 
thus  weakening  it.  Irregularities  are  of  various  kinds. 
Some  of  the  larger  sizes  of  thin-walled  tubing  often  have 
one  half  of  their  walls  much  thicker  than  the  other,  and 
such  tubing  should  only  be  used  for  the  simplest  work. 
Some  tubing  has  occasional  knots  or  lumps  of  unfused 
material.  The  rest  of  the  tube  is  usually  all  right,  but 
often  the  defective  part  must  be  cut  out.  The  presence 
of  striations  running  along  the  tube  is  generally  an  indica- 
tion of  hard,  inferior  glass.  Crookedness  and  non-uni- 
formity of  diameter  are  troublesome  only  when  long 
pieces  must  be  used. 

Devitrification  is  one  of  the  worst  faults  glass  can 
possibly  have.  It  is  especially  common  in  old  glass,  and 
in  glass  which  has  contained  acids.  It  seems  to  be  of  two 
sorts.  One  variety  manifests  itself  on  the  surface  of  the 
glass  before  it  reaches  its  working  temperature,  but  if 
the  glass  be  heated  to  the  highest  temperature  of  the 
flame  it  will  disappear  except  in  the  portion  at  the  edge 
of  the  heated  part.  The  glass  seems  to  work  all  right,  but 


MATERIALS  AND  APPARATUS  3 

an  ugly  crystallized  ring  is  left  at  the  edge  of  the  portion 
heated.  This  kind  appears  most  frequently  in  old  glass 
which  was  originally  of  good  quality,  but  has  in  time  been 
superficially  altered,  probably  by  the  loss  of  alkalies. 
The  other  variety  of  devitrification  does  not  appear 
when  the  glass  is  first  heated;  but  after  it  has  been  main- 
tained at  or  above  its  working  temperature  for  a  longer 
or  shorter  time,  it  will  be  noticed  that  the  outer  surface 
has  lost  its  smoothness,  and  appears  to  be  covered  with 
minute  wrinkles.  It  will  also  be  found  that  the  glass  has 
become  harder,  so  that  it  becomes  impossible  to  work  it 
easily.  Further  heating  only  makes  the  matter  worse, 
as  does  the  use  of  a  higher  temperature  from  the  start. 
In  fact  it  will  often  be  found  that  a  piece  of  compara- 
tively soft  glass  which  devitrifies  almost  at  once  in  a 
" hissing"  flame  can  be  worked  without  serious  difficulty 
if  care  be  taken  to  use  a  flame  still  decidedly  tinged  with 
yellow.  Even  good  glass  will  begin  to  devitrify  in  this 
way  if  heated  too  long  at  the  highest  temperature  of  the 
flame,  so  care  should  always  be  taken  (1)  to  reduce  the 
time  of  heating  of  any  spot  of  glass  to  a  minimum;  i.e.,  get 
the  desired  result  at  the  first  attempt,  if  possible,  or  at 
least  with  the  minimum  of  reheating  and  " doctoring," 
and  (2)  avoid  keeping  the  glass  at  the  highest  temperature 
of  the  flame  any  longer  than  necessary.  This  may  be 
accomplished  by  doing  all  heating,  shrinking,  etc.,  of  the 
glass  in  a  flame  more  or  less  tinged  with  yellow,  and  only 
raising  the  temperature  to  the  highest  point  when  ready 
to  blow  the  glass.  This  kind  of  devitrification  is  appar- 
ently due  to  volatilization  of  the  alkalies  from  the  glass  in 
the  flame,  and  it  is  said  that  it  can  be  partly  remedied  or 
prevented  by  holding  a  swab  of  cotton  saturated  with  a 
strong  solution  of  common  salt  in  the  flame  from  time  to 
time  as  the  glass  is  heated. 
The  toughness  of  glass,  i.e.,  its  ability  to  withstand 


4          LABORATORY  MANUAL  OF  GLASS-BLOWING 

variations  of  temperature,  depends  on  its  composition 
and  the  care  taken  in  its  annealing.  In  general,  largo 
pieces  of  glass  should  be  heated  very  slowly  in  the  smoky 
flame,  and  the  larger  the  diameter  of  the  tube  the  greater 
the  length  which  must  be  kept  warm  to  prevent  cracking. 
All  large  pieces  should  be  carefully  heated  over  their 
whole  circumference  to  the  point  where  the  soot  deposit 
burns  off,  before  being  finally  cooled.  After  being  thus 
heated  they  are  cooled  in  a  large  smoky  flame  until  well 
coated  with  soot,  then  the  flame  is  gradually  reduced  in 
size  and  the  object  finally  cooled  in  the  hot  air  above  it 
until  it  will  not  set  fire  to  cotton.  If  thought  necessary, 
it  may  then  be  well  wrapped  in  cotton  and  allowed  to 
cool  in  the  air.  If  not  properly  annealed  the  place  heated 
may  crack  spontaneously  when  cold,  and  it  is  quite  cer- 
tain to  crack  if  it  is  reheated  later. 

Next  in  importance  to  the  glass  are  the  blow-pipe  and 
the  bellows.  Any  good  blast  lamp,  such  as  is  ordinarily 
used  in  a  chemical  laboratory  for  the  ignition  of  precipi- 
tates, will  be  satisfactory;  provided  it  gives  a  smooth 
regular  flame  of  sufficient  size  for  the  work  in  hand, 
and  when  turned  down  will  give  a  sharp-pointed  flame 
with  well-defined  parts.  Where  gas  is  not  available,  an 
ordinary  gasoline  blow-torch  does  very  well  for  all  opera- 
tions requiring  a  large  flame,  and  a  mouth  blow-pipe 
arranged  to  blow  through  a  kerosene  flame  does  well  for 
a  small  flame.  Several  dealers  make  blow-torches  for 
oil  or  alcohol  which  are  arranged  to  give  a  small  well- 
defined  flame,  and  they  would  doubtless  be  very  satis- 
factory for  glass-work.  Any  good  bellows  will  be 
satisfactory  if  it  does  not  leak  and  will  give  a  steady 
supply  of  air  under  sufficient  pressure  for  the  maximum 
size  of  flame  given  by  the  lamp  used.  A  bellows  with  a 
leaky  valve  will  give  a  pulsating  flame  which  is  very 
annoying  and  makes  good  work  very  difficult.  When 


MATERIALS  AND  APPARATUS  5 

compressed  air  is  available  it  can  be  used,  but  if  possible 
it  should  be  arranged  so  that  the  supply  can  be  controlled 
by  the  foot,  as  both  hands  are  usually  needed  to  hold  the 
work.  For  the  same  reason  the  supply  of  air  is  usually 
regulated  by  varying  the  rate  of  operation  of  the  bellows, 
rather  than  by  adjusting  the  valve  of  the  blast-lamp. 
On  the  other  hand,  it  will  be  found  best  to  always  adjust 
the  flow  of  the  gas  by  means  of  the  cock  on  the  lamp, 
rather  than  that  at  the  supply  pipe.  The  operator  must 
have  complete  control  over  the  flame,  and  be  able  to 
change  its  size  and  character  at  short  notice  without 
giving  the  work  a  chance  to  cool,  and  often  without  ceas- 
ing to  support  it  with  both  hands. 

Glass-blowing  should  be  done  in  a  good  light,  but  pref- 
erably not  in  direct  sunlight.  The  operator  should  be 
seated  in  a  chair  or  on  a  stool  of  such  a  height  that  when 
working  he  may  comfortably  rest  one  or  both  elbows  on 
the  table.  The  comfort  of  the  operator  has  a  decided 
influence  on  the  character  of  his  work;  especially  in  the 
case  of  a  beginner,  who  often  defeats  his  purpose  by 
assuming  uncomfortable  and  strained  positions.  Steadi- 
ness and  exact  control  of  both  hands  are  essential  in  most 
operations;  any  uncomfortable  or  strained  position  tires 
the  muscles  and  weakens  the  control  of  the  operator  over 
them. 

In  the  arrangement  of  the  exercises  here  presented, 
several  factors  have  been  considered.  It  is  important 
that  the  first  exercises  be  simple,  although  not  necessarily 
the  simplest,  and  they  should  teach  the  fundamental 
operations  which  will  be  used  and  amplified  later.  They 
should  in  themselves  be  things  which  are  of  importance 
and  commonly  used  in  glass-work,  and  they  should  be  so 
arranged  that  the  fundamental  points,  such  as  the  rota- 
tion of  glass,  the  proper  temperature,  blowing  and  shrink- 
ing the  glass  may  be  learned  with  a  minimum  expenditure 


6          LABORATORY  MANUAL  OF  GLASS-BLOWING 

of  time,  glass  and  gas.  It  is  therefore  recommended  that 
the  beginner  take  them  up  in  the  order  given,  at  least  as 
far  as  No.  7,  and  that  each  be  mastered  before  attempting 
the  next.  The  beginner  should  not  leave  the  first  exer- 
cise, for  example,  until  he  can  join  together  two  pieces 
of  tubing  so  that  they  form  one  piece  of  substantially 
uniform  inner  and  outer  diameter,  and  without  thick  or 
thin  spots.  From  two  to  four  practice  periods  of  two 
hours  each  should  suffice  for  this.  This  chapter  and  the 
following  one  should  also  be  frequently  read  over,  as  many 
of  the  points  discussed  will  not  be  understood  at  first  and 
many  of  the  manipulations  described  will  not  be  necessary 
in  the  simpler  exercises. 


CHAPTER  II 

GENERAL  OPERATIONS 

Cutting  the  Glass. — For  this  purpose  a  "  glass-knife  " 
is  preferred  to  a  file,  if  the  glass  is  cold:  if  it  is  hot  a  file 
must  always  be  used,  and  its  edge  slightly  moistened  to 
prevent  drawing  the  temper.  The  glass-knife  is  simply 
a  flat  piece  of  hard  steel,  with  the  edges  ground  sharp  on 
an  emery  wheel.  The  bevel  of  the  edge  should  be  from 
30  to  60  degrees.  An  old  flat  file  can  easily  be  ground 
into  a  suitable  knife.  The  glass-knife  makes  a  narrower 
scratch  than  the  file  but  appears  more  likely  to  start  the 
minute  crack  which  is  to  cause  the  tube  to  break  at  that 
point,  and  the  break  is  more  likely  to  give  a  good  square 
end.  The  scratch  should  be  made  by  passing  part  of 
the  knife  or  file  once  across  the  glass,  never  by  " sawing" 
the  tool  back  and  forth.  This  latter  procedure  dulls  the 
tool  very  quickly. 

In  breaking  a  piece  of  glass  tubing,  many  persons  for- 
get that  it  is  necessary  to  pull  the  ends  apart,  as  well  f 
as  to  bend  the  tube  very  slightly  in  such  a  direction  as  to 
open  up  the  minute  crack  started  in  the  scratch.  Care 
in  breaking  the  tube  is  essential,  as  it  is  impossible  to  do 
as  good  work  with  uneven  ends  as  with  square  ones. 

When  tubing  of  large  diameter  or  thin  wall  is  to  be  cut, 
it  is  often  better  not  to  attempt  to  break  it  in  the  usual 
way,  but  to  heat  a  very  small  globule  of  glass  (1/16  to  1/8 
inch  diameter)  to  red  heat,  and  touch  it  to  the  scratch. 
This  will  usually  start  the  crack  around  the  tube;  if  it 
has  not  proceeded  far  enough,  or  has  not  gone  in  the  de- 

7 


8          LABORATORY  MANUAL  OF  GLASS-BLOWING 

sired  direction,  it  may  be  led  along  with  a  hot  point  of 
glass.  This  is  put  a  little  beyond  the  end  of  the  crack, 
and  as  the  latter  grows  out  toward  it,  moved  along  the 
path  where  the  crack  is  desired.  This  point  of  glass  is 
also  very  useful  in  breaking  off  very  short  ends  of  tubes, 
where  there  is  not  room  to  get  a  firm  enough  hold  and 
sufficient  leverage  to  break  the  tube  in  the  ordinary 
way,  and  for  breaking  tubes  attached  to  large  or  heavy 
objects,  which  would  be  likely  to  make  trouble  if  treated 
in  the  ordinary  way. 

Another  way  of  cutting  large  tubing,  especially  if  it 
has  rather  thick  walls,  is  to  make  a  scratch  in  the  usual 
way,  and  then  turn  on  the  smallest  and  sharpest  possible 
flame  of  the  blast  lamp.  The  tube  is  next  taken  in  both 
hands  and  held  horizontally  above  the  flame  so  that  the 
scratch  is  exactly  over  it.  The  tubing  is  now  rotated 
rapidly  about  its  axis,  and  lowered  so  that  the  flame  is 
just  tangent  to  its  lower  side.  After  about  ten  seconds 
of  heating,  it  is  removed  from  the  flame  and  the  hot  por- 
tion quickly  breathed  upon,  when  it  will  generally  crack 
apart  very  nicely.  Care  must  be  taken  to  hold  the  tube 
at  right  angles  to  the  flame  during  the  heating,  and  to 
rotate  it  so  that  only  a  narrow  strip  of  the  circumference 
is  heated,  and  the  scratch  should  be  in  the  center  of  this 
heated  strip.  By  this  means  tubing  as  large  as  two  inches 
in  diameter  is  readily  broken. 

Griffin's  glass  cutter,  which  contains  a  hardened  steel 
wheel,  like  that  on  any  ordinary  window-glass  cutter,  and 
a  device  by  which  this  can  be  made  to  make  a  true  cut 
clear  around  the  tube,  is  a  very  handy  article,  especially 
for  large  tubing,  and  may  be  obtained  from  any  dealers 
in  chemical  apparatus. 

Bending  Glass. — Inasmuch  as  this  is  one  of  the  com- 
monest operations  in  the  laboratory,  it  is  assumed  that 
the  reader  knows  how  to  perform  it.  However,  it 


GENERAL  OPERATIONS  9 

should  be  noted  that  in  order  to  obtain  the  best  results 
a  broad  (fish-tail  burner)  flame  should  generally  be  used, 
and  the  tube  rotated  on  its  axis  during  the  heating,  and 
allowed  to  bend  mostly  by  its  own  weight.  If  large  tub- 
ing  is  to  be  bent,  one  end  must  be  stoppered  and  great 
care  used.  Whenever  the  tube  shows  signs  of  collapsing 
or  becoming  deformed,  it  must  be  gently  blown  out  into 
shape,  heating  the  desired  spot  locally  if  necessary.  A 
blast-lamp  is  likely  to  be  more  useful  here  than  the  fish- 
tail burner. 

Drawing  Out  a  Tube. — Most  students  learn  this  the 
first  day  of  their  laboratory  work  in  chemistry,  but  few 
take  pains  to  do  it  well.  The  tube  should  be  heated  in 
the  flame  of  a  Bunsen  burner,  or  blast  lamp  (preferably 
the  latter)  until  it  is  very  soft.  During  this  time  it  must 
be  continuously  rotated  about  its  axis,  and  so  held  that 
the  edges  of  the  heated  zone  are  sharply  defined;  i.e., 
it  should  not  be  allowed  to  move  back  and  forth  along 
its  own  axis.  When  so  hot  that  it  cannot  longer  be  held 
in  shape,  the  tube  is  removed  from  the  flame,  and  the 
ends  slowly  and  regularly  drawn  apart,  continuing  the 
rotation  of  the  tube  about  its  axis.  By  regulating  the  rate 
of  drawing  and  the  length  of  tube  heated,  the  desired 
length  and  diameter  of  capillary  may  be  obtained.  The 
tube  should  always  be  rotated  and  kept  in  a  straight  line 
until  the  glass  has  set,  so  that  the  capillary  may  have  the 
same  axis  as  the  main  tube.  This  capillary  or  "tail" 
is  often  a  very  necessary  handle  in  glass-blowing,  and  if 
it  is  not  straight  and  true,  will  continually  make  trouble. 

In  drawing  out  very  large  tubing,  say  from  one  to 
.two  inches  in  diameter,  it  is  often  necessary  to  draw  the 
tube  in  the  flame,  proceeding  very  slowly  and  at  a 
lower  temperature  than  would  be  used  with  small  tub- 
ing. This  is  partly  on  account  of  the  difficulty  of  heat- 
ing large  tubing  uniformly  to  a  high  temperature,  and 


10       LABORATORY  MANUAL  OF  GLASS-BLOWING 

partly  in  order  to  prevent  making  the  conical  part  of 
the  tube  too  thin  for  subsequent  operations. 

Constricting  a  Tube. — Where  a  constriction  is  to  be 
made  in  a  tube,  the  above  method  must  be  modified,  as 
the  strength  of  the  tube  must  be  maintained,  and  the 
constricted  portion  is  usually  short.  Small  tubes  are 
often  constricted  without  materially  changing  their  out- 
side diameter,  by  a  process  of  thickening  the  walls.  The 
tube  is  heated  before  the  blast  lamp,  rotating  it  about 
its  axis  as  later  described,  and  as 
it  softens  is  gradually  pushed 
together  so  as  to  thicken  the  walls 
at  the  heated  point,  as  in  a,  Fig.  1. 
When  this  operation  has  proceeded 
far  enough,  the  tube  is  removed 
from  the  flame,  and*  the  ends  cau- 
tiously and  gently  drawn  apart, 

continuing  the  rotation  of  the  tube 
FIG.  1. — Constricting  a       ,  .  .  ,       ,  . 

tube  about  its  axis  and  taking  care  not 

to  draw  too  rapidly  at  first.     The 

resulting  tube  should  have  a  uniform  exterior  diameter, 
as  shown  in  b,  Fig.  1. 

This  method  of  constriction  is  not  suited  to  tubes 
much  over  1/4  inch  in  diameter,  since  the  mass  of  glass 
in  the  constricted  part  becomes  so  thick  as  to  be  difficult 
to  handle  when  hot,  and  likely  to  crack  on  cooling. 
Larger  tubes  are  therefore  constricted  by  heating  in  a 
narrow  flame,  with  constant  rotation,  and  when  soft, 
alternately  gently  pulling  the  ends  apart  and  pushing 
them  together,  each  motion  being  so  regulated  that  the 
diameter  of  a  short  section  of  the  tube  is  gradually  re- 
duced, while  the  thickness  of  the  wall  of  the  reduced 
portion  remains  the  same  as  that  of  the  rest  of  the  tube, 
or  increases  only  slightly.  This  pulling  and  pushing  of 
the  glass  takes  place  in  the  flame,  while  the  rotation  is 


GENERAL  OPERATIONS  11 

being  continued  regularly.  The  result  may  appear  as 
indicated  in  c,  Fig.  1.  The  strength  of  the  work  depends 
upon  the  thickness  of  the  walls  of  the  constricted  portion, 
which  should  never  be  less  than  .that  in.  the  main  tube, 
and  usually  a  little  greater.  This  operation  is  most 
successful  with  tubing  having  a  relatively  thin  wall. 

Flanging  a  Tube. — This  operation  produces  the  char- 
acteristic flange  seen  on  test-tubes,  necks  of  flasks,  etc., 
the  object  being  twofold:  to  finish  the  end  neatly  and  to 
strengthen  it  so  that  a  cork  may  be  inserted  without 
breaking  it.  This  flanging  may  be  done  in  several  ways. 
In  any  case  the  first  operation  is  to  cut  the  tube  to  a 
square  end,  and  then  heat  this  end  so  that  the  extreme 
sixteenth  or  eighth  of  an  inch  of  it  is  soft  and  begins  to 
shrink.  The  tube  is  of  course  rotated  during  this  heat- 


FIG.  2. — Flanging  tool. 

ing,  which  should  take  place  in  a  flame  of  slightly  greater 
diameter  than  the  tube,  if  possible.  The  flange  is  now 
produced  by  expanding  this  softened  part  with  some 
suitable  tool.  A  cone  of  charcoal  has  been  recommended 
for  this  purpose,  and  works  fairly  well,  if  made  so  its 
height  is  about  equal  to  the  diameter  of  its  base.  The 
tube  is  rotated  and  the  cone,  held  in  the  other  hand,  is 
pressed  into  the  open  end  until  the  flange  is  formed.  A 
pyramid  with  eight  or  ten  sides  would  probably  be  better 
than  the  cone. 

A  better  flanging  tool  is  made  from  a  triangular  piece 
of  copper  or  brass,  about  1/16  inch  thick,  and  mounted 
in  a  suitable  handle.  Such  a  tool  is  shown  in  Fig.  2, 
being  cut  from  a  sheet  of  copper  and  provided  with  a 


12        LABORATORY  MANUAL  OF  GLASS-BLOWING 

handle  made  by  wrapping  asbestos  paper  moistened  with 
sodium  silicate  solution  about  the  shank  of  the  tool. 
It  is  well  to  have  several  sizes  and  shapes  of  these  tools, 
for  different  sizes  of  tubing.  The  two  sizes  most  used 
will  be  those  having  about  the  following  dimensions: 
(1)  a  =  2  inches,  6  =  1  inch;  (2)  a  =  l  inch,  6  =  1  inch. 
When  the  end  of  the  tube  is  softened,  the  tool  is  inserted 


FIG.  3. — Flanging  a  tube  with  flanging  tool. 

at  an  angle,  as  indicated  in  Fig.  3,  and  pressed  against 
the  soft  part,  while  the  tube  is  quickly  rotated  about  its 
axis.  If  the  flange  is  insufficient  the  operation  may  be 
repeated.  The  tool  should  always  be  warmed  in  the 
flame  before  use,  and  occasionally  greased  by  touching 
it  to  a  piece  of  wax  or  paraffin.  After  the  flange  is  com- 
plete, the  end  must  be  heated  again  to  the  softening  tem- 
perature and  cooled  slowly,  to  prevent  it  from  cracking 


FIG.  4. — Flanging  a  tube  with  carbon  rod  or  wire. 

Some  glass-blowers  use  a  small  carbon  rod,  about 
3/16  inch  in  diameter,  as  a  flanging  tool  for  tubes  larger 
than  about  3/8  inch  diameter,  and  a  small  iron  wire  or 
similar  piece  of  metal  for  smaller  tubes.  In  this  case  the 
tube  is  heated  as  above  described,  and  the  rod  or  wire 
inserted  in  the  end  at  an  angle  and  pressed  against  the 
softened  part,  as  indicated  in  Fig.  4,  while  the  tube  is 


GENERAL  OPERATIONS  13 

rotated  about  its  axis.  For  large  heavy  tubes  a  larger 
carbon  would  be  used. 

Rotation  of  the  Tube.— This  is  the  fundamental  ma- 
nipulation in  glass-blowing,  and  upon  it  more  than  all 
else  depends  the  uniformity  and  finish  of  the  work,  and 
often  the  possibility  of  accomplishing  the  work  at  all. 
Directions  for  it  will  be  given  on  the  assumption  that 
the  reader  is  right-handed;  if  otherwise,  the  position  of 
the  hands  is  of  course  reversed.  The  object  of  rotation 
is  to  insure  even  heating  of  the  whole  circumference  of 
the  tube  at  the  point  of  attack,  to  equalize  the  effect  of 
gravity  on  the  hot  glass  and  prevent  it  from  falling  out  of 
shape  when  soft,  and  to  keep  the  parts  of  the  tube  on 
each  side  of  the  heated  portion  in  the  same  straight  line. 

In  rotating  the  tube,  both  hands  must  be  used,  so  that 
the  two  ends  may  revolve  at  the  same  rate  and  the  glass 
in  the  hot  part  not  be  twisted.  The  rotation  is  performed 
by  the  thumb  and  first  finger  of  each  hand,  the  other 
fingers  serving  to  support  the  tube.  As  it  is  almost 
always  necessary  to  follow  rotating  and  heating  a  tube  by 
blowing  it,  the  hands  should  be  so  placed  that  it  will  be 
easy  to  bring  the  right-hand  end  up  to  the  mouth  without 
shifting  the  hold  on  the  glass.  For  this  reason  the  left 
hand  grasps  the  glass  with  the  palm  down,  and  the  right 
hand  with  the  palm  turned  toward  the  left.  If  there  is 
any  choice,  the  longer  and  heavier  part  of  the  tube  is 
usually  given  to  the  left  hand,  and  it  is  planned  to  blow 
into  the  shorter  end.  This  is  because  it  is  easier  to 
support  the  tube  with  the  hand  which  has  the  palm 
down.  This  support  is  accomplished  by  bending  the 
hand  at  the  wrist  so  that  it  points  slightly  downward,  and 
then  curling  the  second,  third  and  little  fingers  in  under 
the  tube,  which  is  held  between  them  and  the  palm. 
This  support  should  be  loose  enough  so  that  the  thumb 
and  first  finger  can  easily  cause  the  tube  to  rotate  regu- 


14        LABORATORY  MANUAL  OF  GLASS-BLOWING 

larly  on  its  axis,  but  firm  enough  to  carry  all  the  weight 
of  the  tube,  leaving  the  thumb  and  first  finger  nothing 
to  do  but  rotate  it.  The  hand  must  be  so  turned,  and 
the  other  fingers  so  bent,  that  the  thumb  and  first  finger 
stretch  out  nearly  to  their  full  length  to  grasp  the  tube 
comfortably. 

The  right  hand  is  held  with  the  palm  toward  the  left, 
the  fingers  except  the  first  slightly  bent,  and  the  tube 
held  between  the  first  finger  and  the  thumb  while  it 
rests  on  the  second  finger  and  that  portion  of  the  hand 
between  the  base  of  the  first  finger  and  the  thumb. 
Rotation  of  the  tube  is  accomplished  by  rolling  it  between 
the  thumbs  and  first  fingers :  the  rotation  being  continued 
in  the  same  direction  regularly,  and  not  reversed.  It 
is  better  to  roll  slowly  and  evenly,  with  a  series  of  light 
touches,  each  of  which  moves  the  tube  a  little,  than  to 
attempt  to  turn  the  tube  a  half  a  revolution  or  so  with 
each  motion  of  the  hands.  The  hands  must  be  held 
steady,  and  the  tube  must  be  under  good  control  at  all 
times,  so  that  both  ends  may  be  rotated  at  the  same  angu- 
lar velocity,  even  though  they  may  be  of  different  diame- 
ters, and  the  tube  be  neither  drawn  apart  nor  pushed 
together  unless  such  a  motion  is  expressly  desired,  as  it 
sometimes  is.  The  hot  part  of  the  glass  must  be  con- 
stantly watched  to  see  that  it  is  uniformly  rotated  and 
not  twisted,  nor  pulled  out  or  pushed  together  more  than 
is  desired.  Care  must  also  be  taken  to  keep  the  parts  of 
the  tube  in  the  same  straight  line,  or  as  near  it  as  possible, 
during  the  heating  and  all  other  manipulations. 

When  flanging  a  tube,  it  is  held  and  rotated  with  the 
left  hand  as  above  described,  while  the  right  hand  holds 
the  flanging  tool. 

When  part  of  the  end  of  a  tube  must  be  heated,  as  in 
Exercise  6,  and  rotation  must  be  very  carefully  performed 
and  continued  during  the  blowing,  both  hands  are  used. 


GENERAL  OPERATIONS  15 

The  right  hand  is  held  as  above  described,  and  the  left 
hand  close  to  it  and  either  as  above  described  or  else 
with  the  palm  toward  the  right,  grasping  the  tube  in  the 
same  way  as  the  right  hand  does.  This  puts  both  hands 
in  a  position  where  the  tube  may  be  blown  and  rotated 
uniformly  while  its  axis  is  kept  horizontal. 

Smoothness  and  exactness  are  the  two  things  for  which 
the  beginner  must  constantly  strive  in  glass-blowing,  and 
they  are  only  attained  by  a  careful  attention  to  the 
details  of  manipulation,  with  a  steady  hand  and  watchful 
eye.  Every  move  must  count,  and  the  exercise  must  be 
finished  with  a  minimum  of  reheating  and  retouching,  for 
the  best  results. 


CHAPTER  III 

ELEMENTARY  EXERCISES 

EXERCISE  NO.  1 

JOINING  Two  PIECES  OF  TUBING,  END  TO  END — FIRST 
METHOD 

This  exercise  is  most  easily  learned  on  tubing  with  an  ex- 
terior diameter  of  1/4  inch,  or  a  little  less,  having  moder- 
ately heavy  walls.  A  piece  of  such  tubing  is  heated  before 


FIG.  5. — Softening  ends  of  two  pieces  of  tubing. 

the  blow-pipe  at  a  point  ten  or  twelve  inches  from 
the  end,  and  there  drawn  out  to  a  capillary  as  previously 
described  (page  9).  The  capillary  is  sealed  off  about 
two  inches  from  the  main  tube,  and  the  latter  is  cut  near 
the  middle.  Care  should  be  taken  to  get  square  ends 

16 


ELEMENTARY  EXERCISES 


17 


where  the  cut  is  made  (page  7).  The  flame  is  now  so 
regulated  that  it  is  a  little  broader  than  the  diameter  of 
the  tube,  the  sealed  half  of  the  tube  taken  in  the  left 
hand  and  the  other  half  in  the  right.  The  open  end  of 
the  sealed  part  and  one  of  the  ends  of  the  other  part 
are  now  held  in  opposite  sides  of  the  flame,  inclined  at  a 
slight  angle  to  one  another  as  indicated  in  Fig.  5,  and 
rotated  and  heated  until  the  surfaces  of  both  ends  are 
just  softened.  The  two  ends  are  then  carefully  and 


FIG.  6. — Joining  two  pieces  of  tubing  ,end  to  end— first  method. 


quickly  brought  together  (a,  Fig.  6),  removed  from  the 
flame  and  pulled  apart  a  little,  to  reduce  the  lump  formed 
at  the  joint  as  much  as  possible,  as  indicated  in  b.  The 
joint  is  then  tested  by  blowing  into  the  open  end  of  the 
tube  to  see  if  it  is  tight.  If  so,  the  flame  is  reduced  to 
half  or  less  than  half  of  its  former  size,  and  the  joint 
heated  in  it,  holding  the  tube  and  continually  rotating  it 
as  directed  in  the  last  chapter  (page  13). 

As  the  tube  softens  and  tends  to  shrink,  the  two  ends 
are  pressed  together  a  little  and  the  walls  allowed  to 


18        LABOKATOKY  MANUAL  OF  GLASS-BLOWING 

thicken  slightly,  as  in  c.  It  is  then  quickly  removed 
from  the  flame  and  gently  blown  as  indicated  in  d, 
continuing  the  rotation  of  the  tube  during  the  blowing, 
and  at  the  same  time  pressing  the  ends  of  the  tube  to- 
gether a  little  so  as  to  make  a  short  thick-walled  bulb. 
The  joint  is  then  returned  to  the  flame  and  reheated, 
rotating  as  before,  shrinking  to  about  the  shape  of  e. 
When  this  stage  is  reached,  the  glass  should  be  very  hot 
and  fluid,  and  the  mass  of  hot  glass  thick  enough  to 
remain  at  its  working  temperature  for  about  five  seconds 
after  removal  from  the  flame.  The  glass  is  now  reblown 
as  indicated  in/,  to  form  a  bulb  having  walls  of  practically 
the  same  thickness  as  the  original  tube.  As  soon  as  the 
bulb  is  blown,  the  tube  is  removed  from  the  mouth,  held 
horizontally  in  front  of  the  worker,  and  gently  drawn  out 
to  form  one  continuous  tube,  as  indicated  in  g.  During 
both  the  blowing  and  drawing  of  this  bulb  the  rotation 
must  be  continued,  and  both  blowing  and  drawing  must 
be  carefully  regulated  so  that  the  resulting  tube  may  have 
the  same  internal  and  external  diameter  at  the  joint  as 
elsewhere. 

Discussion. — In  making  the  original  joint,  (a,  Fig.  6), 
care  should  be  taken  that  the  lump  formed  is  as  small  as 
possible  so  that  it  may  be  entirely  removed  during  the 
subsequent  operations.  For  this  reason,  only  the.  very 
tip  ends  of  the  two  pieces  of  tubing  are  held  in  the  flame, 
and  the  softening  should  not  extend  more  than  1/16 
inch  down  the  tube.  As  soon  as  the  ends  are  sufficiently 
soft  to  stick  together,  they  are  made  to  do  so.  The  first 
drawing  of  the  tube  (6)  should  take  place  immediately, 
and  reduce  the  lump  as  much  as  possible  without  making 
the  adjacent  walls  of  the  tube  thin.  The  whole  purpose 
of  the  rest  of  the  manipulation  is  to  absorb  or  "iron  out" 
the  lump  at  the  joint.  For  this  reason,  care  is  taken  that 
this  lump  is  always  in  the  center  of  the  flame  while  the 


ELEMENTARY  EXERCISES  19 

joint  is  being  heated,  and  a  small  flame  is  used  so  that 
little  of  the  main  tube  may  be  softened.  During  the  first 
shrinking  of  the  joint  (c)  the  walls  next  the  lump,  being 
thinner  than  it  is,  reach  the  softening  temperature  first 
and  are  thickened  by  the  slight  pushing  together  of  the 
ends,  so  that  they  taper  from  the  lump  to  the  unchanged 
wall.  Upon  blowing  this  joint,  these  thickened  walls 
blow  out  with  the  lump,  but  as  they  are  thinnest  next  the 
unchanged  tube,  they  stiffen  there  first.  Then  as  the 
thicker  parts  are  still  hot,  these  blow  out  more,  and  with 
the  lump  make  a  more  or  less  uniform  wall.  By  this  first 
operation  most  of  the  lump  will  have  been  removed,  pro- 
vided it  was  not  too  large  at  first,  and  the  tube  was  hot 
enough  when  it  was  blown.  Beginners  almost  invariably 
have  the  glass  too  cool  here,  and  find  difficulty  in  blowing 
out  a  satisfactory  bulb.  Under  such  circumstances  the 
lump  will  be  scarcely  affected  by  the  operation. 

During  the  shrinking  of  this  bulb,  the  thinner  parts  of 
course  are  the  first  to  reach  the  softening  point,  and  thus 
contract  more  than  the  thick  parts,  so  that  practically  all 
of  the  lump  can  be  absorbed,  and  a  uniformly  thickened 
part  of  the  tube  left  as  in  e.  When  this  is  just  accom- 
plished, the  second  bulb  must  be  blown  during  one  or 
two  seconds,  and  the  tube  then  drawn  out  as  described, 
so  as  to  change  the  bulb  to  a  tube.  The  drawing  must 
proceed  with  care :  portions  nearest  the  unchanged  tubes 
are  the  first  to  reach  the  proper  diameter,  and  must  be 
given  time  to  just  set  at  that  point  before  the  center  of 
the  bulb  is  finally  drawn  into  shape.  The  drawing  is 
perhaps  best  done  intermittently  in  a  series  of  quick 
pulls,  each  drawing  the  tube  perhaps  1/16  inch,  and  each 
taking  place  as  the  thumbs  and  first  fingers  grasp  the  tube 
for  a  new  turn  in  the  rotation.  If  the  tube  is  not  rotated 
during  the  blowing,  the  bulbs  will  be  lop-sided  and  it  will 
be  impossible  to  get  a  joint  of  uniform  wall-thickness; 


20        LABORATORY  MANUAL  OF  GLASS-BLOWING 

if  rotation  is  omitted  during  the  drawing,  the  tube  will 
almost  invariably  be  quite  crooked. 

If  the  lump  still  shows  distinctly  after  the  operations 
described,  the  cross-section  of  the  tube  will  be  as  in  h,  and 
the  tube  will  be  likely  to  break  if  ever  reheated  at  this 
point  after  it  becomes  cold.  The  operations  d,  e,  f,  and 
g  may  be  repeated  upon  it,  and  it  may  be  possible  to  get 
it  to  come  out  all  right. 

Care  must  be  taken  not  to  blow  the  bulbs  d  and  /  too 
thin  as  they  then  become  very  difficult  to  handle,  and  the 
joint  is  usually  spoiled.  The  wall-thickness  of  these 
bulbs  must  never  be  much  less  than  that  of  the  original 
tube.  If  the  joint  as  completed  has  thinner  walls  than 
the  rest  of  the  tube,  it  will  be  more  easily  broken.  It 
should  be  remembered  that  the  length  of  the  finished 
tube  must  be  exactly  the  same  as  that  of  the  original 
piece,  if  the  walls  of  the  joint  are  to  be  of  their  original 
thickness.  Therefore  the  pushing  together  during  the 
two  operations  c  and  d  must  shorten  the  tube  just  as 
much  as  the  final  drawing  (/  to  g)  lengthens  it. 

The  interval  between  the  removal  of  the  work  from 
the  flame  and  the  beginning  of  the  blowing  must  be  made 
as  short  as  possible,  or  else  the  portions  next  the  main 
parts  of  the  tube  will  set  before  they  can  be  blown  out, 
and  cause  irregular  shrunken  areas. 

EXERCISE  NO.  2 

JOINING  Two  TUBES  END  TO   END — SECOND   METHOD 

The  method  described  in  Exercise  No.  1  is  very  satis- 
factory for  joining  short  lengths  of  straight  tubing,  but 
becomes  inconvenient  or  impossible  when  the  pieces  are 
long  or  bent,  on  account  of  the  difficulty  in  uniformly 
rotating  such  work.  In  such  cases,  this  second  method  is 


ELEMENTARY  EXERCISES  21 

used.  It  does  not  usually  give  as  smooth  and  pretty  a 
joint  as  the  first  method,  and  takes  a  little  longer. 

The  joint  is  begun  exactly  as  in  the  first  method,  and 
the  manipulation  is  the  same  until  after  the  preliminary 
tight  joint  (6,  Fig.  6)  is  made.  The  flame  is  reduced  as 
usual,  but  instead  of  rotating  the  tube  in  the  flame,  only 
one  part  of  the  circumference  is  heated,  and  this  is 
allowed  to  shrink  thoroughly  before  blowing.  It  is  then 
blown  gently  so  that  it  becomes  a  slight  swelling  on  the 
tube,  and  the  operation  repeated  on  an  adjoining  part  of 
the  joint.  Three  or  four  repetitions  of  the  operation  will 
usually  cover  the  whole  circumference  of  the  joint,  in  a 
small  tube,  the  result  being  a  swelling  roughly  similar 
to  the  first  thick  bulb  in  the  first  method  (d,  Fig.  6).  If 
all  the  lumps  of  the  original  joint  have  not  been  removed 
by  this  operation,  it  may  now  be  repeated  upon  such  parts 
as  may  require  it.  The  thickness  of  the  wall  in  the  bulb 
should  be  about  the  same  as  that  in  the  original  tube. 
The  whole  of  the  expanded  joint  is  now  heated  as  uni- 
formly as  may  be  until  soft  enough  so  that  it  begins  to 
shrink  a  little,  and  the  swelling  is  gently  drawn  down  to 
the  same  diameter  as  the  main  tube,  as  in  the  first  case. 
Any  irregularities  in  the  finished  joint  may  be  corrected 
by  local  reheating,  shrinking  or  blowing  as  required. 

Discussion. — In  using  this  method,  especially  with 
larger  sizes  of  tubing,  it  is  very  important  to  keep  the 
whole  circumference  of  the  joint  hot  enough  during  the 
operation  so  that  it  does  not  crack  apart  at  the  part 
which  has  not  yet  been  worked.  For  that  reason  the 
first  heating,  shrinking  and  blowing  should  be  performed 
as  quickly  as  possible,  leaving  the  resulting  irregularities 
to  be  corrected  later,  rather  than  attempting  to  reblow 
the  same  part  of  the  joint  several  times  in  succession 
until  it  is  satisfactory.  Care  must  be  taken  in  this  as  in 
the  first  method  that  the  blowing  follows  immediately 


22       LABORATORY  MANUAL  OF  GLASS-BLOWING 

upon  the  completion  of  the  shrinking  and  removal  of 
the  object  from  the  flame:  delay  in  blowing  will  cause 
shrunken  places  where  the  joint  meets  the  original  tubes, 
on  account  of  the  cooling  and  setting  of  the  glass  before 
it  was  blown.  Most  beginners  err  in  being  afraid  to 
shrink  the  part  of  the  joint  enough  before  blowing  it. 
On  small  tubing,  the  shrinkage  may  often  extend  so  far 
that  the  inner  surface  of  the  shrunken  part  reaches  the 
center  of  the  tube.  Insufficient  shrinking  results  in 
failure  to  remove  the  lump  formed  at  the  original  joint. 
It  is  often  of  advantage,  after  blowing  out  part  of  the 
joint,  to  allow  that  part  a  few  seconds  to  set  before  going 
on  with  the  rest,  keeping  the  whole  joint  warm  meanwhile 
in  or  near  the  smoky  flame.  This  helps  to  prevent  the 
twisting  of  the  joint,  or  other  distortion  incident  to  the 
handling  of  a  piece  of  work  of  awkward  shape. 

In  making  a  joint  on  a  very  long  or  heavy  piece  by 
this  method,  it  is  often  advantageous  to  attach  a  piece 
of  rubber  tubing  to  the  open  end,  hold  the  other  end  of 
this  tubing  in  the  mouth  during  the  process,  and  blow 
through  it,  rather  than  attempt  to  bring  the  end  of  the 
glass  up  to  the  mouth.  This  enables  one  to  keep  closer 
watch  on  the  joint,  and  avoid  drawing  it  out  or  distorting 
it  in  handling.  On  the  other  hand,  the  rubber  tube  is  an 
inconvenience  on  account  of  its  weight  and  the  conse- 
quent pull  on  the  end  of  the  apparatus,  and  makes  rota- 
tion difficult. 

EXERCISE  NO.  3 

THE  "TEE"  TUBE 

The  operations  involved  are  two:  the  blowing  of  a 
short  side  tube  on  a  piece  of  tubing,  and  sealing  another 
piece  of  tubing  on  this,  by  what  is  essentially  the  second 
method  as  just  described. 


ELEMENTARY  EXERCISES 


23 


The  two  pieces  of  tubing  to  be  used  each  have  one  end 
cut  square  and  the  other  sealed  in  the  usual  manner. 
The  longer  of  the  two  is  now  heated  at  the  point  at  which 
the  joint  is  to  be  made,  until  it  begins  to  color  the  flame. 
A  small  flame  is  used,  and  the  tube  rotated  until  the 
flame  begins  to  be  colored,  when  the  rotation  is  stopped, 
and  only  one  spot  heated  until  a  spot  the  diameter  of  the 
tube  to  be  sealed  on  has  become  red  hot  and  begun  to 
shrink.  This  is  now  gently  blown  out  into  a  small  bulb, 
as  in  a,  Fig.  7,  and  it  will  be  noted 
that  this  bulb  will  have  walls  tap- 
ering from  the  thick  walls  of  the 
tube  to  a  very  thin  wall  at  the 
top.  The  sides  of  this  bulb,  be- 
low the  dotted  line,  are  to  form 
the  small  side  tube  to  which  the 
main  side  tube  is  to  be  sealed. 
The  top  of  the  bulb  is  now  soft- 
ened by  directing  a  small  flame 
directly  upon  it,  and  as  soon  as 
it  shrinks  to  the  level  indicated 
by  the  dotted  line,  it  is  removed 
from  the  flame  and  quickly  blown 
out  to  form  a  thin  bulb,  as  indi- 
cated in  b,  Fig.  7.  This  will  usu- 
ally be  so  very  thin  that  a  stroke  of  the  file  or  glass- 
knife  will  break  it  off  at  the  dotted  line,  leaving  the 
side  tube,  to  which  the  short  piece  of  tubing  is  now 
sealed  according  to  the  second  method  (Exercise  No  2). 
In  doing  this,  care  is  taken  to  direct  the  flame  partly  on 
the  main  tube  in  the  two  crotches,  so  that  both  tubes  blow 
out  a  little  and  give  space  for  the  gases  to  turn  in,  as 
indicated  in  c,  Fig.  7,  and  at  the  same  time  increase  the 
mechanical  strength  of  the  job.  On  the  other  hand, 
care  is  taken  not  to  deform  the  main  tube,  and  not  to 


FIG.  7.— The  "tee"  tube- 


24       LABORATORY  MANUAL  OF  GLASS-BLOWING 

produce  such  a  bulge  or  bulb  at  the  joint  as  will  prevent 
the  finished  tube  from  lying  flat  on  a  table. 

Discussion. — Most  beginners  tend  to  err  in  the  first 
steps  of  this  operation,  by  blowing  too  hard  and  too  long 
when  blowing  out  the  little  bulb.  The  result  is  a  large, 
very  thin  bulb,  which  breaks  off  in  such  a  way  as  to  leave 
a  hole  in  the  main  tube,  occupying  nearly  half  the  cir- 
cumference of  the  tube  at  that  point,  instead  of  the  neat 
side  tube  which  they  should  have.  It  is  not  difficult  to 
seal  a  tube  on  this  side  tube,  but  it  is  very  difficult  to  seal 
a  tube  into  a  hole  in  another  tube.  Care  should  be  taken 
here,  as  in  the  two  previous  exercises,  that  the  lump 
obtained  at  the  joint  when  the  two  tubes  are  put  together 
is  made  as  small  as  possible,  and  reduced  if  possible  by 
gently  drawing  on  the  side  tube  as  soon  as  the  tubes  have 
actually  joined.  It  is  much  easier  to  prevent  the  forma- 
tion of  a  lump  at  the  joint  than  it  is  to  remove  the  lump 
after  it  is  formed.  The  remarks  previously  made  about* 
blowing  quickly  after  removing  the  work  from  the  flame 
apply  here  with  especial  force.  A  "tee"  tube,  from  its 
very  nature,  is  exposed  to  a  good  many  strains,  so  care 
must  be  taken  that  the  walls  of  the  joint  are  of  uniform 
thickness  with  the  rest  of  the  tube. 

The  beginner  will  find  it  easiest  to  make  this  tube  out 
of  two  pieces  of  the  same  tube,  about  1/4  inch  in  diameter. 
Larger  or  smaller  tubing  is  usually  more  difficult.  If 
tubing  much  more  than  1/4  inch  is  used,  the  whole  joint, 
including  part  of  the  main  tube,  must  be  heated  nearly 
to  the  softening  point  at  the  close  of -the  operation,  and 
well  annealed,  as  described  in  Chapter  I  (page  3)  or  it 
will  be  almost  certain  to  crack.  In  the  larger  sizes  of 
tube  it  will  be  necessary  to  heat  the  whole  circumference 
of  the  main  tube  frequently  during  the  operation,  to 
prevent  it  from  cracking. 

In  sealing  a  small  tube  on  the  side  of  a  large  one,  it  is 


ELEMENTARY  EXERCISES  25 

usually  advisable,  after  warming  the  spot  where  the  joint 
is  to  be  made,  to  attach  a  small  drop  of  glass  to  the  tube 
at  that  point,  and  direct  the  flame  upon  that,  thus  supply- 
ing at  the  same  time  both  a  definite  point  to  be  heated 
and  an  extra  supply  of  glass  for  the  little  side  tube  which 
is  desired.  In  this  way  it  is  also  easier  to  blow  out  a 
side  tube  with  a  sufficiently  small  diameter.  If  the 
diameter  of  this  tube  should  be  much  greater  than  that 
of  the  small  tube,  the  latter  may  be  enlarged  with  a 
carbon  or  a  flanging  tool. 

EXERCISE  NO.  4 

To  JOIN  Two  TUBES  OF  DIFFERENT  DIAMETERS 

In  this  case  the  first  method  (Exercise  No.  1)  is  to  be 
used  whenever  possible,  as  it  gives  a  much  smoother  joint 
than  the  second  method.  The  directions  given  will 
'describe  the  adaptation  of  this  method  to  the  problem: 
if  the  second  method  must  be  used  on  account  of  awk- 
ward shape,  etc.,  of  the  work,  the  modifications  required 
will  be  obvious  to  any  one  who  has  learned  to  make  the 
joint  by  the  first  method. 

After  sealing  or  corking  one  end  of  the  larger  tube,  the 
other  end  is  drawn  out  to  form  a  tail  as  described  on  page 
9,  taking  care  to  have  the  tube  uniformly  heated,  and 
to  draw  the  tail  rapidly  enough  so  that  the  cone  is  short, 
as  indicated  in  a,  Fig.  8.  The  tube  is  now  rotated,  a 
small  flame  directed  against  the  cone  at  right  angles 
to  an  element  of  it,  and  it  is  allowed  to  shrink  a  little, 
as  indicated  in  6,  Fig.  8,  so  that  its  walls  will  thicken. 
When  the  tail  is  cut  off,  at  the  dotted  line,  the  diameter 
of  the  opening  and  the  thickness  of  the  walls  at  that  point 
should  correspond  with  the  dimensions  of  the  tube  to  be 
sealed  on.  As  the  glass  is  hot,  the  scratch  for  cutting  it 
must  be  made  with  a  file  (moisten  the  edge!),  and  it 


26       LABORATORY  MANUAL  OF  GLASS-BLOWING 

often  will  not  break  square  across.  Before  proceeding 
to  seal  on  the  small  tube,  any  large  projections  on  the 
cut  end  are  best  removed,  by  warming  the  cut  surface  a 
little,  directing  the  small  flame  upon  each  projection  in 
turn  and  touching  it  with  a  warm  scrap  of  glass.  It  will 
adhere  to  this  and  may  then  be  removed  by  rotating  this 
scrap  a  little  so  as  to  wind  up  the  projection  on  it,  and 
then  drawing  it  off,  while  the  flame  is  still  playing  on  the 
spot.  This  must  be  done  rapidly  and  care  taken  not  to 
soften  the  main  part  of  the  cone. 


FIG.  8. — Joining  two  tubes  of  different  diameters. 

The  large  tube  is  now  taken  in  the  left  hand,  the  small 
one  in  the  right,  the  ends  heated  and  joined  in  the  usual 
manner,  taking  care  not  to  get  any  larger  lump  at  the 
joint  than  necessary.  A  small  flame  is  now  directed  on 
the  cone  at  right  angles  to  its  elements  as  before,  and  the 
tube  rotated  so  as  to  heat  the  whole  circumference.  The 
flame  should  be  just  large  enough  to  heat  the  whole  of 
the  cone.  As  the  latter  shrinks,  the  lump  at  the  joint 
is  brought  into  the  edge  of  the  flame,  and  it  and  a  very 
little  of  the  small  tube  allowed  to  shrink  with  the  cone. 


ELEMENTARY  EXERCISES  27 

When  well  shrunk  and  heated  to  blowing  temperature 
the  joint  is  removed  from  the  flame  and  blown  gently 
with  careful  rotation,  pushing  the  tubes  together  a  little 
when  the  blowing  is  about  finished,  so  that  the  cone 
becomes  a  short  thick  half-bulb,  as  shown  in  d,  Fig.  8. 
This  corresponds  to  the  first  thick  bulb  in  the  first  method 
(dj  Fig.  6),  and  is  treated  similarly.  It  is  again  heated 
and  shrunk,  taking  care  not  to  involve  either  the  large 
tube  or  the  small  one  in  the  shrinking,  blown  quickly  to 
about  the  same  shape  as  before,  (d,  Fig.  8),  and  then 
gently  drawn  out  into  a  smooth  cone  (e) ,  exactly  as  in  the 
first  exercise.  Care  should  be  taken  not  to  draw  too 
rapidly  or  too  far,  as  then  the  resulting  cone  (/)  is  weaker 
than  it  should  be,  and  does  not  look  well. 

Discussion. — The  beginner  will  find  that  this  operation 
is  best  learned  on  two  tubes  which  are  not  too  nearly  of 
the  same  diameter.  A  tube  about  5/8  inch  in  diameter 
and  one  a  little  less  than  1/4  inch  will  be  suitable.  Both 
should  have  moderately  heavy  walls  (1/16  inch  or  a 
trifle  over  for  the  large  tube,  and  a  trifle  less  for  the  small 
one)  but  the  large  tube  should  not  be  too  heavy  or  else  it 
will  be  hard  to  prevent  melting  down  too  much  of  the 
small  tube,  and  getting  this  drawn  out  too  thin  during  the 
process.  One  of  the  troublesome  features  of  this  exercise 
is  the  difficulty  of  rotating  two  tubes  of  different  diameters 
with  the  same  angular  velocity,  so  as  not  to  twist  the 
joint.  Another  difficulty  is  found  in  getting  the  cone 
uniformly  heated  to  blowing  temperature  without  over- 
heating and  overshrinking  the  small  tube.  The  reason 
for  this  is  obviously  the  much  greater  circumference  of 
the  cone,  especially  at  its  large  end,  so  that  relatively 
much  less  of  it  is  being  heated  at  any  time.  The  beginner 
is  also  inclined  to  start  with  too  long  a  cone,  or  else  heat 
so  much  of  the  large  tube  that  part  of  its  glass  is  included 
in  the  cone,  with  the  result  that  in  order  to  get  the 


28        LABORATORY  MANUAL  OF  GLASS-BLOWING 

right  wall-thickness  the  cone  must  be  made  too  long  (g, 
Fig.  8).  This  does  not  look  well,  and  usually  will  be 
irregular  in  shape. 

EXERCISE  NO.  5 

TUBE  FOR  CONDENSING  SULPHUR  DIOXIDE 

This  is  useful  as  a  test  of  mastery  of  the  preceding 
exercise.  A  piece  of  3/16  or  7/32  inch  tubing  is  joined 
to  each  end  of  a  piece  of  tubing  5/8  by  about  5  inches,  and 
two  constrictions  made  in  the  large  tube,  by  the  method 
described  on  page  10.  The  small  tubes  are  then  bent 


FIG.  9. — Tube  for  condensing  sulphur  dioxide. 

in  the  same  plane,  as  shown,  and  their  ends  fire-polished 
(Fig.  9). 

EXERCISE  NO.  6 

BULB  AT  THE  END  OF  A  TUBE 

For  this  exercise  tubing  of  1/4  inch  diameter  and  moder- 
ately strong  walls  is  selected.  A  tail  is  drawn  out  on  one 
end  of  the  tube,  and  a  piece  of  tubing  about  nine  or  ten 
inches  long  is  cut  off.  The  tail  should  be  carefully  drawn 
in  the  axis  of  the  tube,  and  in  the  same  straight  line  with 
it,  as  it  is  to  be  used  as  a  handle  in  assembling  the  glass 
for  the  bulb.  This  tail  must  be  long  enough  so  that  it 
can  be  conveniently  held  in  the  left  hand,  as  described  on 
page  13,  and  rotated  about  the  same  axis  as  the  main 
tube.  Holding  the  main  tube  in  the  right  hand  and  the 
tail  in  the  left,  the  tube  is  rotated  in  a  large  flame  so 


ELEMENTARY  EXERCISES 


29 


that  a  piece  of  it,  beginning  where  the  tail  stops  and 
extending  about  an  inch  to  the  right,  may  be-  uniformly 
heated  to  the  highest  temperature  at  which  it  can  be 
kept  in  shape.  As  soon  as 
this  temperature  is  reached, 
the  tube  is  removed  from  the 
flame,  continuing  the  rotation 
and  taking  care  not  to  draw 
out  the  heated  part,  and 
gently  blown.  The  rotation 
is  carefully  continued  during 
the  blowing,  holding  the  tube 
in  approximately  a  horizontal 
position.  As  soon  as  the  tube 
has  expanded  a  little  the  tail 
is  pushed  gently  toward  the 
main  tube,  continuing  the 
gentle  blowing.  If  this  is 
properly  done,  the  heated 
piece  of  tube  will  become  a 
short  bulb  of  about  double  its 
original  diameter,  and  about 
the  same  wall  thickness  as  the 
original  tube.  It  will  have 
somewhat  the  appearance  of 
a,  Fig.  10,  when  properly  ma- 
nipulated. 

The  tube  is  now  reheated  as  before,  taking  care  this 
time  that  the  heating  extends  over  all  that  part  of  the 
bulb  to  the  right  of  the  dotted  line  in  the  figure,  as  well 
as  part  of  the  main  tube  adjoining.  If  this  heating  has 
been  properly  placed,  when  the  operation  of  blowing  and 
pushing  together  is  repeated  the  result  will  be  to  lengthen 
the  bulb  into  a  uniform  cylinder,  as  shown  in  6,  Fig.  10. 
Otherwise  the  result  will  be  a  series  of  bulbs,  as  in  e, 


FIG.  10  — Blowing  a  bulb  on 
the  end  of  a  tube. 


30        LABORATORY  MANUAL  OF  GLASS-BLOWING 

Fig.  10,  separated  by  thickened  ridges  which  will  be 
almost  impossible  of  removal  later  and  will  disfigure  the 
final  bulb.  This  operation  of  heating,  blowing  and 
pushing  together  is  repeated  several  times,  until  the 
cylinder  becomes  as  long  as  can  be  conveniently  handled 
(about  1  1/4  inches  to  1  1/2  inches).  If  more  glass  is 
needed  than  is  then  contained  in  the  cylinder,  the  latter 
may  now  be  heated  as  a  whole,  and  blown  and  pushed 
gently  into  a  shorter  cylinder  of  a  slightly  greater  diame- 
ter, and  more  glass  then  added  as  before. 

When  enough  glass  has  been  collected  for  the  bulb,  it 
is  all  well  heated  and  blown  gently  a  couple  of  times, 
pushing  the  mass  together  as  required,  until  a  thick  bulb 
like  d,  Fig.  10,  is  obtained.  The  tail  must  now  be 
removed  at  the  point  indicated  by  the  dotted  line.  To 
do  this,  a  very  fine  flame  is  directed  on  the  point  where 
the  tail  joins  the  bulb,  and  the  tube  well  rotated  as  the 
glass  softens  at  that  point.  When  sufficiently  soft,  the 
work  is  raised  a  little,  so  that  the  flame  instead  of  striking 
the  glass  squarely  at  the  point  indicated  passes  below  and 
tangential  to  it.  The  tail  is  now  drawn  off  slowly,  con- 
tinuing the  rotation,  raising  the  work  just  out  of  the 
flame  whenever  the  thread  of  glass  drawn  off  becomes  too 
thin,  and  lowering  it  again  to  the  point  where  the  flame 
just  touches  it  when  the  glass  stiffens  a  little.  By  this 
means  the  tail  may  be  drawn  off  without  leaving  an 
appreciable  lump  behind,  as  indicated  in e and/,  Fig.  10. 
When  as  much  of  the  extra  glass  has  been  removed  as  is 
practicable,  the  flame  is  brought  to  play  squarely  upon 
the  little  lump  left,  the  last  of  the  tail  removed,  and  the 
lump  heated  and  gently  blown  to  a  small  excrescence  on 
the  main  bulb.  The  whole  end  of  the  latter  is  now  heated 
until  it  begins  to  shrink  a  little,  and  gently  blown  to 
make  it  uniform  in  thickness.  The  whole  bulb  is  then 
heated  in  a  flame  of  the  proper  size,  so  that  it  all  may 


ELEMENTARY  EXERCISES  31 

shrink  to  about  two-thirds  of  its  diameter.  The  flame 
must  be  very  carefully  chosen  and  directed,  so  as  to 
shrink  all  the  bulb,  right  up  to  the  main  tube,  but  not 
soften  the  latter.  As  soon  as  this  stage  is  reached,  the 
bulb  is  removed  from  the  flame,  continuing  the  even 
rotation,  and  blown  to  the  desired  size,  preferably  by  a 
series  of  gentle  puffs  following  one  another  at  very  short 
intervals.  During  the  blowing,  the  main  tube  is  held  in 
a  horizontal  position,  and  any  tendency  of  the  bulb  to 
fall  out  of  line  is  corrected  by  the  rotation.  If  the  shape 
of  the  bulb  or  its  size  are  not  satisfactory,  it  may  be 
shrunk  again  and  reblown.  Such  shrinking  should  begin 
in  a  large  yellow  flame,  with  just  enough  air  to  give  it 
direction.  The  amount  of  air  may  be  gradually  increased 
as  the  bulb  shrinks  and  the  walls  become  thick  enough  to 
bear  it  without  collapsing.  If  the  bulb  starts  to  collapse 
at  any  time,  it  must  be  immediately  blown  enough  to 
regain  its  convex  surface,  before  the  shrinking  proceeds 
further. 

Discussion. — In  collecting  the  glass  for  the  bulb, 
enough  must  be  gathered  to  give  the  walls  the  desired 
strength.  Since  the  area  of  a  sphere  is  proportional  to 
the  cube  of  its  diameter,  it  is  evident  that  doubling  the 
size  of  a  bulb  diminishes  the  thickness  of  its  walls  to  a 
very  large  extent.  The  limit  of  diameter  for  a  strong 
bulb  on  ordinary  1/4-inch  tubing,  collecting  the  glass  as 
above,  is  about  1  1/2  inches,  and  the  beginner  will  do  well 
not  to  blow  his  bulbs  more  than  an  inch  in  diameter. 

The  collection  of  the  glass  is  one  of  the  most  important 
parts  of  the  process.  If  the  mass  of  glass  be  twisted,  fur- 
rowed or  ridged,  or  lopsided,  it  is  very  difficult  to  get  a 
good,  even,  spherical  bulb,  no  matter  how  many  times  it 
is  shrunk  and  blown.  The  greatest  care  should  therefore 
be  taken  to  get  a  uniform  cylinder,  on  the  same  axis  as 
the  main  tube;  and  to  this  end  the  rotation  of  the  tube 


32        LABORATORY  MANUAL  OF  GLASS-BLOWING 

must  be  carried  on  very  evenly.  For  method  of  holding 
the  tube,  see  page  14. 

If  a  very  large  bulb  is  required,  it  will  often  be  econom- 
ical to  seal  on  the  end  of  the  tube  a  short  piece  of  a  large 
tube,  provided  with  the  proper  tail,  and  use  the  glass  in 
the  large  tube  for  the  bulb  instead  of  attempting  to  col- 
lect it  from  the  small  tube.  In  this  case  part  of  the  small 
tube  will  usually  be  included  in  the  bulb,  so  that  the  joint 
comes  in  the  latter,  and  not  where  it  joins  the  tube.  As 
the  amount  of  glass  carried  on  the  end  of  the  tube 
increases  in  weight  and  size  the  difficulties  of  heating  it 
uniformly,  keeping  it  in  the  proper  position  and  handling 
it  increase  rapidly. 

In  collecting  glass,,  it  is  usually  best  not  to  leave  the 
part  of  the  cylinder  next  the  tube  with  too  thick  walls. 
This  is  always  the  coolest  part  during  the  preparation  for 
blowing  the  bulb,  consequently  it  does  not  get  blown  out, 
and  causes  an  ugly  thickened  appearance  on  that  end  of 
the  bulb. 

If  the  bulb  grows  too  long  or  pear-shaped,  it  may  be 
easily  shortened  by  heating  to  the  blowing  temperature, 
and  then  blowing  gently  with  the  main  tube  in  a  vertical 
position,  and  the  bulb  at  the  top  of  it.  Gravity  will  then 
shorten  the  bulb  nicely. 

The  finished  bulb  should  be  a  nearly  perfect  sphere, 
with  the  axis  of  the  tube  passing  through  its  center,  and 
the  portion  of  the  tube  adjoining  the  bulb  must  not  be 
distorted,  twisted,  or  blown  out.  In  order  to  prevent  the 
distortion  of  the  tube,  care  must  be  taken  that  it  is  never 
heated  quite  to  its  softening  point  during  the  process. 

EXERCISE  NO.  7 
BLOWING  A  BULB  IN  A  TUBE 

The  tube  is  selected  and  one  end  closed  as  in  the  pre- 
vious exercise,  but  it  should  be  cut  a  little  longer,  say 


ELEMENTARY  EXERCISES  33 

about  twelve  inches.  Beginning  at  a  point  about  four 
inches  from  the  closed  end,  glass  is  collected  and  blown  in- 
to a  thick-walled  bulb,  exactly  as  in  the  previous  exercise. 
Greater  care  must  be  taken,  however,  that  the  cylinder 
collected  and  this  thick  bulb  are  of  uniform  thickness  and 
set  squarely  in  the  axis  of  the  tube.  Instead  of  removing 
the  tail,  the  bulb  must  be  blown  in  this  case  with  both 
pieces  of  tubing  attached,  and  care  must  be  taken  that 
they  "line  up"  properly,  i.e.,  are  in  the  same  straight 
line,  and  that  this  line  passes  as  near  as  may  be  through 
the  center  of  the  bulb.  The  tube  is  held  in  approximately 
horizontal  position  during  the  blowing  of  the  bulb,  as  in 
the  previous  case,  and  especial  care  taken  with  the  rota- 
tion. Both  pieces  of  tube  must  of  course  be  rotated  at 
the  same  rate,  and  their  softened  ends  must  be  kept  at 
exactly  the  proper  distance  from  each  other,  so  that  the 
bulb  may  be  spherical  and  not  elongated.  If  the  blow- 
ing of  the  bulb  be  quickly  and  accurately  done,  it  may 
usually  be  completed  before  the  glass  is  quite  set,  and*  the 
alignment  of  the  two  tubes  may  then  be  rectified  while 
looking  straight  through  the  bore  of  the  tube. 

Discussion. — The  two  points  of  greatest  importance 
are  the  collection  of  the  glass,  and  the  uniform  rotation 
of  the  tube.  A  larger  tube  may  be  sealed  in  the  middle  of 
a  small  one  when  a  large  amount  of  glass  is  necessary. 
The  piece  of  tubing  used  for  the  exercise  must  be  long 
enough  so  that  the  fingers  may  be  kept  on  a  cool  part  of 
the  glass  without  getting  uncomfortably  near  the  ends 
of  the  tube.  It  should  not  be  any  longer  than  necessary, 
however,  as  the  extra  weight  and  length  make  the  ma- 
nipulation of  the  hot  glass  more  difficult. 

When  a  string  of  bulbs  are  required  on  the  same  tube,  a 
piece  of  glass  18  inches  long  may  be  used  at  the  start, 
and  the  first  bulb  made  near  the  closed  end,  as  described. 
Each  succeeding  bulb  will  then  be  in  plain  view  during  the 


34        LABORATORY  MANUAL  OF  GLASS-BLOWING 

blowing,  and  when  the  open  end  becomes  too  short  for 
comfort,  it  may  be  dried  out,  cut  off,  and  another  piece 
joined  to  it,  starting  as  in  the  first  method  (Exercise 
No.  1),  but  instead  of  drawing  out  the  thick  bulb  to  a 
tube,  it  is  made  part  of  the  glass  collected  for  the  next 
bulb.  If  the  string  of  bulbs  becomes  awkward  to  handle 
on  account  of  its  length  and  weight,  it  may  be  made  in 
several  parts  and  these  later  sealed  together  by  the  second 
method,  preferably  blowing  through  a  rubber  tube  at- 
tached to  the  open  end,  as  described  on  page  22. 

Very  neat  small  bulbs  may  be  made  on  tubing  of  a 
diameter  of  3/16  inch  or  a  little  less,  but  the  beginner  is 
advised  to  start  with  tubing  of  about  1/4  inch  diameter. 
The  use  of  tubing  with  too  thick  walls  usually  produces 
bulbs  which  are  thick-walled  at  the  point  where  they 
leave  the  tube,  but  inclined  to  be  too  thin  at  the  point  of 
maximum  diameter  (perpendicular  to  the  axis  of  the  tube) 
where  most  of  the  strain  comes  and  strength  is  par- 
ticularly needed. 


CHAPTER  IV 

ADVANCED  EXERCISES 

EXERCISE  NO.  8 

SEALING  A  TUBE  THROUGH  ANOTHER  TUBE 
First  Method — Making  a  Gas-washing  Tube 

This  first  method  can  be  used  whenever  one  can  work 
through  an  open  end  opposite  to  the  end  of  the  tube 
where  the  joint  is  to  be  made.  To  illustrate  it,  take  a 
piece  of  rather  thin-walled  tubing,  about  3/4  inch  in 
diameter,  and  some  pieces  of  rather  strong  tubing  a  little 
less  than  1/4  inch  in  diameter.  Draw  off  the  large  tube 
in  a  short  cone,  then  draw  off  the  tail  as  in  the  making  of 
the  bulb  on  the  end  of  the  tube,  blow  out  the  little  lump 
slightly,  shrink  the  whole  cone  a  little  and  blow  gently  to 
form  a  rounded  end  like  that  on  a  test-tube,  with  walls 
about  the  thickness  of  those  of  the  rest  of  the  tube.  Cut 
this  tube  to  a  suitable  length,  say  about  six  inches,  and  pro- 
vide two  corks  which  will  fit  the  open  end  of  it.  Now  cut 
a  piece  of  the  small  tubing  of  the  proper  length  to  form 
the  piece  which  is  to  be  inside  the  large  tube.  For  prac- 
tice purposes,  this  piece  should  be  about  an  inch  shorter 
than  the  large  tube.  Flange  one  end  of  this  tube  a  little, 
and  anneal  the  flange  well  in  the  smoky  flame.  Bore  one 
of  the  corks  so  that  a  piece  of  the  small  tubing  will  fit  it, 
and  cut  a  couple  of  notches  in  the  side  of  this  cork  so  that 
air  can  pass  between  it  and  the  glass.  Pass  a  short  piece 
of  the  small  tubing  through  this  cork,  and  attach  the 

35 


36 


LABORATORY  MANUAL  OF  GLASS-BLOWING 


flanged  piece  of  small  tube  to  this  by  means  of  a  short 
piece  of  rubber  tubing,  so  that  when  the  whole  is  inserted 
in  the  large  tube  it  is  arranged  as  in  a,  Fig.  11.  The  piece 
of  glass  tubing  projecting  out  through  the  cork  is  now  cut 
off  so  as  to  leave  an  end  about  1/2  inch  long  when  the 
cork  is  firmly  seated  and  the  inner  tube  pushed  into 
contact  with  the  center  of  the  end  of  the  large  tube,  as 


D 


FIG.  11. — Gas-washing  tube. 

shown  in  the  drawing.  Care  should  be  taken  that  the 
little  rubber  tube  which  joins  the  two  pieces  is  arranged 
as  in  the  figure;  i.e.,  most  of  it  on  the  piece  of  tubing  which 
passes  through  the  cork,  and  very  little  on  the  other 
piece,  so  that  when  the  cork  is  removed  after  the  small 
tube  has  been  sealed  through  the  large  one,  the  rubber 
tube  may  easily  come  with  it.  Select  a  short  piece  of  the 
small  tubing  of  suitable  length  for  the  piece  which  is  to 


ADVANCED  EXERCISES  37 

be  on  the  outside  of  the  large  tube  as  a  continuation  of 
the  piece  inside,  and  another  piece  for  the  delivery  tube. 
A  small  bulb  may  be  blown  in  the  latter  at  a  point  about 
21/2  inches  from  the  closed  end,  and  the  open  end  cut 
off  about  1  1/2  inches  from  the  bulb.  A  cork  or  cork- 
boring  of  suitable  size  to  stopper  the  small  tube  is  pre- 
pared, and  laid  ready  with  the  other  (unbored)  cork  for 
the  large  tube. 

When  everything  is  in  readiness,  the  rounded  end  of  the 
large  tube  is  slowly  heated  until  it  softens  and  joins  firmly 
to  the  small  tube  inside.  After  it  has  shrunk  down  well, 
it  is  blown  out  to  its  original  size,  placing  the  whole  end 
of  the  large  tube,  cork  and  all,  in  the  mouth.  Now  with  a 
fine-pointed  flame  the  glass  covering  the  end  of  the  small 
tube  is  heated  to  the  softening  temperature,  and  then  is 
blown  out  to  an  excrescence  by  blowing  on  the  end  of  the 
small  tube  which  passes  through  the  cork.  The  end  of 
this  excrescence  is  heated  and  blown  off  in  the  usual  way, 
so  as  to  leave  the  small  tube  sealed  on  the  inside  of  the 
large  one  and  opening  through  it  into  this  short  tube  which 
has  been  blown  out.  The  end  of  the  small  tube  which 
passes  through  the  cork  is  now  closed  with  the  cork  pre- 
pared for  it,  and  the  short  outer  tube  is  joined  to  the  tube 
that  has  just  been  blown  out,  so  that  the  joint  appears 
like  b,  Fig.  11.  Use  the  first  method  (Exercise  No.  1) 
for  this  joint.  Reheat  the  whole  of  the  end  of  the  tube 
nearly  to  the  softening  temperature,  anneal  it  a  little, 
and  allow  to  cool  a  few  seconds  until  well  set.  Now 
remove  the  cork,  short  glass  tube  and  rubber  tube  from 
the  open  end  of  the  large  tube  and  insert  the  solid  cork 
in  their  place.  Warm  the  joint  and  the  whole  of  that 
end  of  the  tube  again  carefully  up  to  about  the  softening 
point,  then  seal  on  the  side  tube  for  the  delivery  of  the 
gas  in  the  usual  way,  taking  care  that  the  whole  of  the 
end  and  the  joint  are  kept  warm  meanwhile.  When 


38       LABORATORY  MANUAL  OF  GLASS-BLOWING 

thoroughly  sealed,  the  delivery  tube  is  bent  up  parallel 
to  the  tube  through  which  the  gas  enters,  and  then  out 
at  right  angles  to  it,  as  shown  in  c.  The  whole  of  the 
end  of  the  tube  is  now  cautiously  reheated  and  then  cooled 
slowly  to  anneal  it. 

The  cork  may  now  be  removed  from  the  open  end  of 
the  large  tube,  this  end  heated  in  a  large  flame,  caught 
together  with  a  scrap  of  glass  tubing  and  drawn  off  into 
a  cone  so  that  the  base  of  the  cone  is  about  opposite  the 
end  of  the  inner  tube.  The  lump  of  glass  is  drawn  off  the 
point  of  this  cone  and  it  is  reblown  to  form  a  rounded 
end,  as  previously  described. 

After  this  cools,  the  tube  through  which  the  gas  enters 
may  be  heated  at  the  proper  point  and  bent  at  right 
angles  to  form  the  finished  apparatus  as  shown  in  d. 
The  ends  of  the  small  tube  are  cut  off  square  and  fire- 
polished. 

Discussion. — After  the  joint  has  once  been  made,  great 
care  must  be  taken  that  it  is  kept  hot  during  all  the  sub- 
sequent manipulations,  and  if  it  becomes  somewhat 
cool  at  any  time  it  must  be  reheated  very  slowly.  It  is 
obvious  that  the  rate  of  heating  and  cooling  of  the  inner 
tube  will  be  slower  than  that  of  the  outer  tube,  and  this 
will  readily  produce  stresses  which  tend  to  crack  the  tube 
at  the  joint.  The  amount  of  heating  and  cooling  which 
such  a  joint  will  stand  depends  upon  its  form.  The 
beginner  should  examine  such  a  joint  on  regular  factory- 
made  apparatus,  and  note  the  uniformity  of  wall-thick- 
ness and  the  " clean-cut"  appearance  of  the  joint,  as  a 
model  for  his  imitation.  A  ragged  joint,  where  the  line 
of  joining  of  the  inner  and  outer  tubes  wavers  instead  of 
going  squarely  around  the  tube,  is  almost  sure  to  crack 
during  the  cooling  and  heating  unless  extra  precautions 
are  taken  with  it.  The  presence  of  a  small  lump  of  glass 
at  any  point  on  the  joint  affords  an  excellent  starting 


ADVANCED  EXERCISES  39 

place  for  a  crack,  as  do  also  the  points  on  a  ragged  joint 
where  the  inner  tube  comes  farther  down  on  the  outer 
tube  than  at  other  points. 

In  order  to  insure  a  joint  which  is  square  and  not 
ragged,  it  is  essential  that  the  angle  between  the  inner 
and  outer  tubes  at  the  joint  be  very  nearly  a  right  angle. 
For  this  reason  the  two  tubes  should  not  be  of  too  near 
the  same  size,  or  if  this  cannot  be  avoided,  a  small  bulb 
should  be  blown  on  the  end  where  the  joint  is  to  be  made. 
If  this  bulb  be  made  with  the  same  wall-thickness  as  the 
rest  of  the  tube,  and  somewhat  pear-shaped,  it  may  be 
drawn  out  to  the  same  size  as  the  rest  of  the  tube,  if 
necessary,  after  the  joint  has  been  made. 

This  method  is  used  wherever  possible  in  preference  to 
the  second  method  (Exercise  No.  9),  as  it  is  easier  to  get 
a  good  joint  with  it.  It  may  also  be  used  where  it  is 
desired  to  seal  the  tube  through  the  side  of  a  tube,  or  for 
a  tube  sealed  through  the  wall  of  a  bulb,  as  in  a  Geissler 
potash  bulb  or  similar  apparatus.  Where  there  is  not 
space  to  join  the  inner  tube  to  the  blowing  tube  by  a 
rubber  tube,  this  joint  may  be  made  with  a  small  piece 
of  gummed  paper,  which  can  readily  be  broken  when 
desired. 

EXERCISE  NO.  9 

SEALING  A  TUBE  THROUGH  ANOTHER  TUBE 
Second  Method — Making  a  Suction  Pump 

Select  a  piece  of  tubing  3/8  to  1/2  inch  in  diameter, 
with  walls  about  1/16  inch  or  a  little  less  in  thickness, 
heat  a  place  about  4  inches  from  one  end  and  draw  it 
out  so  that  when  cut  off  at  the  proper  point  it  will  look 
like  a,  Fig.  12;  the  open  end  of  the  drawn  out  part  being 
small  enough  to  slip  inside  another  piece  of  the  original 
tube.  A  small  thick-walled  bulb  is  now  blown  as 


40        LABORATORY  MANUAL  OF  GLASS-BLOWING 

indicated  by  the  dotted  lines,  and  annealed.  A  piece  of 
the  original  tubing  is  now  prepared,  7  or  8  inches  long, 
with  one  end  cut  square  off  and  the  other  closed.  A 
piece  of  1/4-in  tubing  about  2  inches  long,  and  drawn  out 
at  one  end  to  a  tail  several  inches  long  is  also  prepared,  to 
form  the  inlet  tube  for  the  air.  Another  piece  of  the 
3/8-inch  tube  is  prepared,  about  4  inches  long,  and  pro- 
vided with  a  tail  drawn  out  as  indicated  in  6,  so  that  when 
cut  off  at  about  2  1/2  or  3  inches  from  the  main  tube  its 
inner  diameter  may  be  slightly  less  than  that  of  the  nar- 
rowest point  of  the  tube  a.  A  small  thick-walled  bulb 
is  blown  at  the  point  indicated  by  the  dotted  lines,  and 


FIG.  12. — Suction  pump. 

annealed.  Care  must  be  taken  in  drawing  the  capillary 
and  blowing  the  bulb  in  both  a  and  b  that  the  capillary 
tubes  are  in  the  axis  of  the  main  tube,  and  in  the  same 
straight  line  with  it. 

The  open  end  of  the  8-inch  piece  of  tube  and  the  bulb 
of  the  piece  a  are  now  warmed  together,  the  end  of  the 
tube  only  moderately  and  the  bulb  to  about  its  softening 
temperature.  The  tube  a  is  now  inserted  in  the  open  end 
of  the  large  tube,  and  the  bulb  softened  with  a  suitable 
flame  and  pressed  into  good  contact  with  the  tube.  It 
is  then  reheated,  including  the  joint,  blown  a  little  and 
pulled  out  to  form  a  straight  tube  in  line  with  the  main 
tube.  By  warming  the  joint  a  little,  and  proper  rotation, 


ADVANCED  EXERCISES  41 

the  capillary  may  be  brought  into  the  same  straight  line 
with  the  rest  of  the  tube. 

Keeping  this  joint  hot,  a  place  about  an  inch  from  it  on 
the  tube  a  is  warmed,  and  the  piece  of  1/4-inch  tubing 
previously  prepared  is  sealed  on  at  that  point.  The 
joint  is  then  well  annealed  and  allowed  to  cool. 

The  tube  a  is  now  cut  at  such  a  place  that  when  b  is 
inserted  in  the  open  end  the  point  will  come  near  the 
end  of  the  constriction  of  a,  as  shown  in  c.  Care  is 
taken  to  get  a  clean  square  cut.  The  side  tube  is  now 
cut  off  about  an  inch  from  the  main  tube  and  corked. 
Tube  b  is  sealed  into  the  open  end  of  a,  in  the  same  way  as 
a  was  sealed  into  the  large  tube,  and  the  joint  carefully 
annealed. 

Discussion. — As  in  the  first  method,  the  secret  of  suc- 
cess lies  in  getting  a  square  joint,  and  having  the  inner 
tube  leave  the  outer  one  at  nearly  right  angles.  All  the 
remarks  about  annealing,  lumps,  etc.,  made  under  the 
previous  method  apply  here. 

This  method  may  be  applied  in  sealing  a  small  tube 
into  the  end  of  a  large  one,  the  latter  being  either  drawn 
to  a  cone  and  cut  off  at  the  desired  diameter,  or  else 
given  a  rounded  end  like  a  test-tube  and  a  hole  the  proper 
size  blown  in  the  center  of  it.  A  suitable  thick-walled 
bulb  is  to  be  blown  on  the  small  tube,  as  in  the  case 
described  above.  This  method  is  also  used  in  making 
the  Kjeldahl  trap  (a,  Fig.  13),  the  small  tube  to  be 
inserted  being  first  drawn,  the  thick  bulb  blown  at  its 
point  of  union  with  the  main  tube,  and  then  the  small 
tube  bent  and  cut.  The  large  bulb  is  best  made  with 
rather  heavy  wall,  being  either  blown  in  the  middle  of 
a  tube,  and  one  piece  of  the  tube  drawn  or  cut  off,  or 
else  made  on  the  end  of  a  tube.  In  the  latter  case  a  drop 
of  glass  must  be  put  on  the  point  where  the  joint  is  to 
be,  so  as  to  get  a  hole  of  the  proper  size  with  enough  glass 


42       LABORATORY  MANUAL  OF  GLASS-BLOWING 

around  it  to  prevent  it  from  growing  larger  when  it  is 
heated.  The  author  prefers  to  blow  the  bulb  in  the 
middle  of  the  tube,  draw  off  one  end  of  the  bulb,  and 
blow  out  the  desired  hole  where  the  tube  was  drawn  off. 
The  whole  bulb  must  generally  be  reheated  and  blown 
a  little  at  the  end  of  the  process,  and  well  annealed. 


FIG.  13. — a,  Kjeldahl  trap;  b,  suction  pump  on  smaller  tubing. 

The  suction  pump  can  also  be  made  on  1/4-inch  tubing, 
and  one  joint  saved  if  desired,  by  constricting  the  tube 
to  form  the  raceway  for  the  water  and  air,  as  shown  in 
6,  Fig.  13.  i,See  page  10  for  method.)  But  it  is  more 
difficult  to  make  a  square  joint  on  such  small  tubing. 


CHAPTER  V 

MODIFIED  METHODS  AND  SPECIAL  OPERATIONS 
CAPILLARY  TUBING 

This  is  commonly  used  in  many  forms  of  apparatus 
for  gas  analysis,  and  one  is  often  called  upon  to  join  two 
pieces  or  to  make  a  tee  on  it.  The  methods  are  nearly 
the  same  as  with  other  tubing,  except  that  more  care  and 
patience  are  required.  The  work  must  be  done  much 
more  slowly  on  account  of  the  thickness  of  the  walls,  and 
open  ends  of  the  tube  must  always 
be  enlarged  before  joining  them  to 
anything.  This  is  best  done  by  care- 
fully sealing  the  end  and  then  blowing, 
with  several  suitable  reheatings,  to 
form  a  pear-shaped  bulb  as  in  a,  Fig. 
14.  The  end  of  this  is  then  heated 
and  blown  off,  and  the  piece  is  ready 

to  be  joined  to  another  similar  end,  or    FIG   14. Capillary 

to  a  piece  of  ordinary  tubing   if  de-  tubing, 

sired.  The  joints  are  best  not  blown 
too  much,  as  thick  walls  shrink  very  slowly.  Much  may 
be  done  by  gently  pushing  the  tube  together  or  pulling 
it  apart  in  the  flame,  to  remove  lumps  and  irregulari- 
ties. It  is  necessary  that  the  bore  of  the  joint  be  ap- 
proximately that  of  the  main  tube,  and  care  must  be 
taken  that  the  latter  is  not  constricted  at  the  point 
where  the  joint  begins. 

Especial  care  must  be  taken  to  warm  the  tube  slowly 
when  starting  and  cool  it  slowly  when  through,  as  the 

43 


44        LABOEATORY  MANUAL  OF  GLASS-BLOWING 

thick  walls  frequently  crack  if  not  carefully  handled. 
For  this  reason  the  whole  neighborhood  of  the  joint  must 
be  heated  somewhat  so  that  there  may  not  be  stresses  set 
up  between  the  heated  and  unheated  portions. 

In  making  the  tee  (6,  Fig.  14)  the  inability  to  blow  the 
joint  makes  itself  decidedly  felt,  but  if  the  side  tube  is 
properly  enlarged  as  previously  described,  a  good  joint 
can  be  made  by  alternately  pulling  and  pushing  on  the 
end  of  the  side  tube,  and  shrinking  well. 

Very  fine  capillary  tubing  should  be  blown  with  a 
rubber  bulb  instead  of  the  mouth,  so  as  not  to  get 
moisture  into  the  tube.  The  rubber  bulb  may  also  be 
used  to  advantage  on  some  of  the  coarser  capillary 
tubing. 

When  a  bulb  is  to  be  joined  to  a  piece  of  capillary 
tubing,  the  joint  is  preferably  made  before  blowing  the 
bulb,  and  will  then  be  taken  up  a  little  way  on  the  bulb 
during  the  process.  Care  must  of  course  be  taken  not  to 
constrict  the  capillary;  the  pear-shaped  bulb  blown  on 
the  end  (a,  Fig.  14)  may  well  extend  back  a  little  further 
than  usual  into  the  tube  so  as  to  prevent  this.  If  a  bulb 
is  required  in  the  middle  of  a  capillary  tube,  the  latter 
is  usually  best  cut  and  a  piece  of  ordinary  tubing  of  suit- 
able size  sealed  in  to  provide  material  for  the  bulb. 

GLASS  ROD 

Joints,  tees,  etc.,  in  glass  rod  are  made  on  the  same 
principle  as  in  tubing,  except  that  of  course  they  cannot 
be  blown,  and  regularity  must  be  obtained  by  accumulat- 
ing a  small  mass  of  uniformly  heated  glass,  and  then 
drawing  it  to  a  suitable  rod,  on  the  same  principle  as 
Exercise  No.  1. 

Great  care  must  be  taken  in  heating  and  cooling  this, 
as  in  the  case  of  the  capillary  tubing,  and  for  the  same 
reasons. 


MODIFIED  METHODS  AND  SPECIAL  OPERATIONS    45 

By  joining  pieces  side  by  side,  pressing  with  carbon 
plates  or  a  plate  and  a  rod,  and  other  suitable  manipula- 
tions, stirrers,  spatulas,  and  other  objects  may  easily 
be  made  from  rod,  and  its  manipulation  is  relatively  easy 
on  account  of  the  fact  that  one  does  not  have  to  worry 
about  the  bore  of  the  tube.  But  the  same  general  rule 
about  not  having  thick  and  thin  spots  in  contact,  and 
making  all  changes  in  diameter  on  a  taper  if  possible 
instead  of  abruptly,  applies  here.  Thick  pieces  will  cool 
and  contract  at  different  rates  from  thin  ones,  and  cracks 
are  likely  to  develop  where  they  join.  Work  which 
has  been  formed  with  any  tool  must  always  be  heated  to 
the  softening  point  afterward  before  allowing  it  to  cool 
in  order  to  remove  the  stresses  caused  by  the  contact  of 
the  tool  with  the  hot  glass. 

When  it  is  necessary  to  join  a  piece  of  rod  to  the  side 
of  a  piece  of  tubing,  the  end  of  the  rod  is  made  very  hot 
while  the  wall  of  the  tube  at  the  spot  desired  is  heated  to 
just  below  the  softening  temperature.  The  rod  can  then 
be  pressed  into  firm  union  with  the  tube  and  drawn  a 
little  to  remove  the  excess  of  glass  without  deforming  the 
tube. 

MENDING  STOPCOCKS 

Mending  the  Plug. — The  plug  of  the  stopcock  occa- 
sionally falls  out  and  is  broken.  If  the  break  is  in  the 
main  part  of  the  plug,  nothing  can  be  done  except  to 
search  for  a  spare  plug  of  suitable  size  and  grind  it  to 
fit,  as  described  below.  If  only  the  little  cross-piece  at 
the  end  is  broken  off,  it  can  easily  be  replaced.  In 
most  ordinary  stopcocks  the  plug  is  solid,  but  the  little 
handle  is  hollow.  What  has  been  said  above  regarding 
care  in  heating  and  cooling  glass  rod  applies  with  especial 
force  here.  It  is  usually  best  to  wind  the  whole  of  the 
plug  with  several  thicknesses  of  asbestos  cord,  leaving 


46        LABORATORY  MANUAL  OF  GLASS-BLOWING 

bare  only  the  end  where  the  handle  is  to  be  joined.  This 
diminishes  the  danger  of  cracking  the  plug  by  too  rapid 
heating,  and  also  makes  it  more  comfortable  to  hold.  A 
piece  of  rather  thick- walled  tubing  of  suitable  diameter  is 
chosen,  drawn  out  so  as  to  have  a  suitable  taper  (taking 
care  to  heat  enough  of  the  tube  so  that  the  capillary  .tail 
has  good  wall-thickness  and  strength),  and  then  a 
corresponding  taper  is  drawn  to  form  the  other  side 
of  the  handle.  The  result  is  shown  in  Fig.  15,  a.  The 
capillary  tail  is  now  heated  and  bent  back  to  form  a 
handle  which  will  be  in  the  same  straight  line  as  the  axis 


FIG.  15. — Stopcock  plug. 

of  the  plug  (6,  Fig.  15)  and  the  main  part  of  the  tube 
drawn  off  at  the  dotted  line,  making  a  neat  seal  at  .that 
point.  The  broken  end  of  the  plug  is  now  slowly  warmed 
in  the  smoky  flame,  the  heat  gradually  increased  by  a 
gentle  stream  of  air  from  the  bellows,  and  the  point  at 
which  this  handle  is  to  be  attached  finally  brought  to 
the  temperature  at  which  the  glass  flows  freely.  In  the 
mean  time,  the  little  handle  has  been  warmed  almost  to 
the  softening  point.  It  is  now  quickly  pushed  into  place 
(c,  Fig.  15),  taking  care  that  its  axis  is  parallel  to  the  hole 
in  the  plug,  and  then  drawn  away  from  the  plug  just 
enough  to  make  a  graceful  neck  instead  of  the  bulging  one 


MODIFIED  METHODS  AND  SPECIAL  OPERATIONS    47 

indicated  by  the  arrow  in  the  figure.  With  a  fine  pointed 
flame  the  little  tail  is  now  drawn  off  at  the  point  indicated 
by  the  dotted  line  (c,  Fig.  15)  and  the  whole  carefully  an- 
nealed. If  necessary,  the  handle  can  be  blown  a  little 
before  the  tail  is  removed.  Local  heating  and  blowing  at 
the  point  where  the  handle  joins  the  plug  is  often  necessary 
in  order  to  make  a  smooth  job. 

Regrinding. — This  is  sometimes  necessary  to  make 
stopcocks  tight,  when  the  grinding  has  not  been  properly 
done  in  the  factory.  For  this,  a  very  little  fine  flour  of 
emery  or  carborundum  is  the  best  and  quickest.  If  this 
is  not  at  hand,  some  clean  sand  may  be  ground  in  an  agate 
mortar,  and  if  possible  sieved.  Only  material  which 
passes  the  100-mesh  sieve  should  be  used.  It  will  be 
ground  still  finer  in  the  process.  For  the  final  polishing, 
a  little  infusorial  earth  or  even  kaolin  will  do. 

The  surface  to  be  ground  is  moistened  with  water  and 
dusted  over  with  a  little  of  the  abrasive.  The  plug  is 
now  inserted  in  the  stopcock,  and  turned  with  a  gentle 
pressure.  This  turning  should  be  in  the  same  direction 
for  several  revolutions,  then  in  the  opposite  direction  for 
several  more  revolutions,  etc.  As  the  abrasive  becomes 
finer  during  the  grinding,  a  little  more  may  be  added  if 
necessary.  In  general,  only  a  little  grinding  will  be 
required,  and  one  small  pinch  of  carborundum  or  emery 
will  be  ample.  The  beginner  usually  grinds  too  much, 
and  with  too  coarse  material.  As  the  grinding  surface 
becomes  dry,  water  is  added  drop  by  drop,  and  the  grind- 
ing continued  until  the  abrasive  seems  to  be  reduced  to 
an  impalpable  powder,  most  of  which  has  been  squeezed 
out  of  the  stopcock.  The  two  surfaces  in  the  stopcock 
are  usually  grinding  upon  each  other  at  this  stage,  and 
inspection  will  show  whether  the  contact  between  them 
is  uniformly  good.  If  not,  the  grinding  must  be  con- 
tinued with  a  little  fresh  abrasive.  If  contact  appears 


48        LABORATORY  MANUAL  OF  GLASS-BLOWING 

to  be  good,  the  surfaces  are  ground  together  for  a  little 
with  practically  no  abrasive,  so  as  to  polish  them,  and 
the  joint  is  then  washed  out  and  tested. 

In  grinding  in  a  new  plug  to  replace  a  broken  one,  the 
plug  selected  should  have  practically  the  same  taper  as 
the  seat  into  which  it  is  to  be  ground,  and  should  be  a 
very  little  too  large.  Care  must  be  taken  to  so  distribute 
the  abrasive  material  as  to  grind  mostly  on  the  places 
where  the  plug  fits  tightly. 

Sealing  on  a  New  Tube. — It  frequently  happens  that 
one  of  the  tubes  of  the  stopcock  is  broken  off  close  to 
the  cock  itself,  and  a  new  one  must  be  joined  to  the 
stub  of  the  old  one.  With  care,  this  may  often  be  suc- 
cessfully done  even  where  the  break  is  within  1/4  inch 
of  the  stopcock.  The  first  step  is  to  clean  and  dry  the 
stopcock,  remove  the  plug,  cork  the  open  ends  of  the 
stopcock  sleeve  and  the  other  tube,  and  wind  a  couple 
of  layers  of  asbestos  cord  carefully  over  the  sleeve  and 
the  most  of  the  corks  which  close  it.  A  suitable  tube, 
having  as  near  as  possible  the  same  diameter  and  wall 
strength  as  the  one  broken  off,  is  selected  and  a  piece 
the  desired  length  cut  off.  The  broken  end  of  the  tube 
on  the  stopcock  is  now  squared  off  as  well  as  possible, 
by  cutting  or  by  heating  and  drawing  off  the  projections, 
and  the  new  tube  sealed  on,  usually  with  the  first  method 
(Exercise  No.  1).  If  the  break  is  very  close  to  the  stop- 
cock, very  little  reheating  and  blowing  can  be  done,  on 
account  of  the  danger  of  getting  the  stopcock  sleeve  out 
of  shape,  and  the  work  must  be  heated  very  slowly  to 
prevent  cracking.  The  main  reliance  is  then  placed  on 
making  a  good  joint  when  the  tubes  are  brought  together, 
and  then  drawing  out  this  joint  a  little,  at  once,  to  get  an 
even  wall. 


MODIFIED  METHODS  AND  SPECIAL  OPERATIONS    49 

CLOSED  CIRCUITS  OF  TUBING. 

In  some  pieces  of  apparatus  closed  circuits  of  circular 
or  rectangular  shape  are  required.  A  similar  problem 
is  involved  in  apparatus  like  the  ordinary  Soxhlet 
extractor,  where  a  small  tube  is  joined  to  the  side 
of  a  large  one,  bent  to  form  a  siphon,  and  attached 
again  to  a  continuation  of  the  original  large  tube. 
The  difficulty  in  all  such  cases  is  to  provide  for  the 
contraction  taking  place  as  the  last  joint  cools.  If 
part  of  the  circuit  has  the  shape  of  the  letter  S,  or  is  a 
spiral,  the  natural  springiness  of  the  glass  will  take  care 
of  this.  If  not,  the  side  of  the  circuit  opposite  to  the 
joint  and  parallel  to  it  must  be  heated  also,  the  two  being 
finally  heated  together  to  the  softening  point  after  the 
joint  is  completed,  and  then  allowed  to  cool  together. 

To  make  the  last  joint,  the  rest  of  the  tube  is  made  in 
approximately  the  desired  form,  the  two  pieces  which  are 
to  be  joined  to  make  the  last  joint  being  just  enough  out 
of  the  desired  position  to  allow  them  to  pass  one  another. 
The  final  joint  is  preferably  made  in  the  middle  of  a 
straight  piece  of  tube,  not  at  a  tee.  The  two  pieces 
which  are  to  be  joined  are  bent  so  as  to  just  pass  each 
other,  marked  at  the  right  point  with  the  glass-knife, 
and  cut  there,  preferably  with  a  small  bead  of  hot  glass. 
One  or  both  of  these  tubes  are  now  warmed  to  the  soften- 
ing point  in  such  a  place  that  the  tubes  can  be  made  to 
meet  properly,  and  the  two  cut  ends  pressed  together. 
They  are  now  warmed  in  the  flame,  and  joined  together, 
either  by  simultaneously  warming  the  opposite  side  of 
the  circuit  or  some  other  suitable  part,  so  as  to  allow  the 
two  ends  to  be  pushed  together  again  after  they  are 
softened,  or  by  gently  touching  the  places  that  do  not 
unite  with  a  hot  bead  of  glass,  and  using  the  glass  to  fill 
up  the  crack  where  the  ends  do  not  quite  meet.  Care 


50       LABORATORY  MANUAL  OF  GLASS-BLOWING 

must  be  taken  not  to  leave  knots  or  lumps  of  glass  in  the 
finished  joint,  and  the  latter  should  be  well  reblown,  and 
if  necessary  left  as  a  small  bulb  or  enlargement,  rather 
than  have  it  have  too  thick  walls. 

SPIRALS 

Spirals  of  glass  tubing  are  probably  best  made  free- 
hand before  the  blow-pipe,  unless  one  has  a  great  many  of 
them  to  make,  and  extreme  accuracy  is  desired.  To 
begin  with,  a  piece  of  tubing  of  the  desired  size  (say  3/16 
inch  in  diameter)  and  a  convenient  length  (about  two  feet) 
is  selected,  one  end  closed,  and  a  right-angle  bend  made 


FIG.  16. — Making  a  spiral. 

about  six  inches  from  the  closed  end.  Holding  the  closed 
end  in  the  left  hand  and  the  long  open  one  in  the  right, 
the  spiral  is  begun.  The  short  closed  end  is  to  be  parallel 
to  the  axis  of  the  spiral,  and  preferably  in  that  axis. 
Using  a  moderate-sized  flame,  of  somewhat  yellow  color, 
and  taking  care  to  heat  the  whole  circumference  of  the 
tube,  the  long  open  end  is  wound  little  by  little  into  a 
spiral  having  the  short  end  a  (Fig.  16)  as  an  axis.  The 
bend  at  6,  where  the  tube  changes  from  the  radius  to  the 
circumference  of  the  circle,  must  be  rather  short,  but 
the  tube  must  not  be  flattened  or  constricted  here. 


MODIFIED  METHODS  AND  SPECIAL  OPERATIONS    51 

Especial  pains  is  to  be  taken  with  the  first  turn  of  the 
spiral  (b  to  c,  Fig.  16),  as  the  shape  of  this  determines  the 
diameter  of  the  whole  spiral,  arid  serves  as  a  guide  for  the 
rest  of  the  turns.  The  winding  of  the  tube  is  best  accom- 
plished, after  a  portion  has  been  softened,  by  slowly 
turning  the  short  end  a  a  little  about  its  own  axis,  while 
the  long  open  end  remains  where  it  was.  This  winds 
the  tube  into  a  spiral,  just  as  if  there  were  a  solid  cylinder 
in  the  center  of  it,  and  this  cylinder  was  being  turned 
about  its  axis,  and  was  winding  up  the  soft  glass  upon  its 
circumference.  As  the  cylinder  is  not  actually  there,  the 
curve  of  the  turns  must  be  carefully  estimated  by  the 


FIG.  17. — Ground  joint. 

eye,  so  that  the  spiral  may  be  uniform  and  moderately 
smooth.  When  the  original  piece  of  tube  has  been  used 
up,  another  piece  is  sealed  on  to  the  open  end,  and  the 
operation  continued  as  far  as  may  be  required. 

GROUND  JOINTS 

It  is  sometimes  required  to  join  two  pieces  of  tubing 
end  to  end,  by  means  of  a  ground  joint.  Whenever 
possible,  a  regular  sealed  joint  should  be  used  instead 
of  this  ground  joint,  as  it  is  quicker  to  make,  and 
more  certain  to  be  tight.  Where  a  ground  joint  is 
necessary,  however,  it  is  best  made  in  the  conical  form 
shown  in  c,  Fig.  17.  If  the  wall  of  the  tube  to  be  used 


52        LABORATORY  MANUAL  OF  GLASS-BLOWING 

is  not  very  thick,  it  is  thickened  by  collecting  glass  as 
for  a  bulb  on  the  ends  of  two  tubes  (Exercise  No.  6),  and 
drawing  to  form  cones  of  suitable  shape  (a  and  b.  Fig.  17) 
and  of  such  relative  sizes  that  a  will  slip  about  half  way 
into  b.  In  order  to  make  a  straight  and  give  it  the  proper 
angle,  it  may  be  rolled  when  hot,  upon  a  hot  plate  of  car- 
bon. Blowing  during  this  rolling  is  often  helpful  to 
remove  depressions.  After  b  has  been  drawn  to  nearly 
the  proper  size  and  shape,  it  may  be  smoothed  by  the  use 
of  a  small  carbon  rod,  held  inside  it  at  a  slight  angle,  or 
better  by  the  use  of  a  truncated  hexagonal  pyramid  of 
carbon,  whose  edges  have  the  proper  slant  to  make  the 
inside  of  the  cone  right.  The  proper  taper  for  both  these 
cones  is  the  same  as  that  used  in  stopcocks  of  similar  size. 
The  hexagonal  carbon  can  easily  be  made  by  carefully 
filing  down  an  electric  light  carbon,  and  finally  impreg- 
nating it  with  paraffin  or  beeswax,  and  is  extremely  use- 
ful wherever  a  conical  surface  has  to  be  formed  from  the 
inside  of  a  tube. 

The  tail  is  allowed  to  remain  on  piece  a,  as  a  sort  of 
guide  in  grinding,  and  should  therefore  be  in  the  axis  of 
the  tube  and  have  rather  thick  walls.  Grind  with  emery 
or  carborundum,  as  described  under  a  previous  head. 
(Regrinding  plug  for  stopcock.)  If  many  such  joints  are 
to  be  made,  it  will  pay  to  have  a  little  sleeve  of  brass  made 
with  the  proper  taper,  and  rough  down  the  plug  a  in  it 
to  about  the  proper  size,  while  b  is  roughed  down  by 
means  of  a  brass  or  iron  plug  having  the  same  taper. 
This  prevents  excessive  grinding  of  one-half  of  the  joint 
in  order  to  remove  a  defect  in  the  other  half,  and  is  the 
method  commercially  used  in  making  stopcocks. 

SEALING  IN  PLATINUM  WIRE 

Very  often  it  is  necessary  to  seal  platinum  wire  into 
the  wall  of  a  tube.  Professional  glass-blowers  usually 


MODIFIED  METHODS  AND  SPECIAL  OPERATIONS    53 


use  a  special  sort  of  glass  ("Einschmelzglas")  which 
is  usually  a  lead  glass,  and  is  made  of  such  composi- 
tion that  it  has  the  same  or  practically  the  same 
coefficient  of  expansion  as  platinum.  A  little  globule 
of  this  glass  is  sealed  into  the  tube  in  such  a  way  that 
it  joins  the  platinum  to  the  glass  of  the  tube.  To  do 
this,  the  small  globule  of  special  glass  is  fused  on  the 
platinum  wire  at  the  proper  point  and  the  tube  into 
which  the  wire  is  to  be  sealed  is  heated  and  a  small  tail 
drawn  out  at  the  point  where  the  wire  is  to  be  inserted. 
The  lump  of  the  special  glass  should  be  from  3/32  to 
1/8  inch  in  diameter,  and  the  tail  drawn  on  the  tube 


FIG.  18. 

should  have  a  slightly  less  diameter  at  the  point  (about 
1/8  inch  or  less  from  the  tube)  where  it  is  cut  off.  There 
are  now  two  ways  of  sealing  in  the  wire.  (1)  The  wire 
with  the  globule  of  glass  is  placed  inside  the  tube  and 
the  latter  revolved  until  the  end  of  the  wire  sticks  out 
of  the  cut  tail  (a,  Fig.  18).  The  latter  is  now  gently 
heated,  and  the  two  glass  surfaces  fused  together,  taking 
care  to  use  only  the  end  of  the  hissing  flame,  if  the  special 
glass  contains  lead.  (See  Chapter  I,  page  1.)  The 
whole  circumference  of  the  tube  is  then  heated  and  an- 
nealed carefully.  (2)  The  end  of  the  wire  which  is  to 
be  outside  the  tube  is  attached  to  the  end  of  a  thin  scrap 


54        LABOKATORY  MANUAL  OF  GLASS-BLOWING 

of  glass,  by  heating  the  glass  and  thrusting  the  wire  into 
it  a  very  little  way.  Using  this  piece  of  glass  as  a  handle, 
the  wire  is  inserted  in  the  cut  tail  (6,  Fig.  18)  and  the 
globule  brought  near  to  the  end  of  the  tail.  (If  the  main 
tube  is  cold,  it  must  of  course  first  be  warmed.)  With 
the  end  of  the  hissing  flame,  as  in  the  first  method,  the 
globule  of  glass  is  melted  and  the  end  of  the  tail  softened. 
The  wire  is  now  pushed  into  place,  the  handle  removed 
by  heating  the  end  and  withdrawing  it,  and  the  tail  re- 
heated a  little  if  necessary  to  make  it  shrink  back  into 
line  with  the  walls  of  the  tube.  The  whole  circumfer- 
ence of  the  tube  is  heated  at  that  point  and  annealed  as 
usual. 

•  The  use  of  this  special  glass  is  not  absolutely  necessary 
if  the  platinum  wire  is  small  (1/4  millimeter  or  less  in 
diameter),  and  in  fact  it  is  often  better  in  such  cases 
not  to  use  it,  unless  the  apparatus  is  to  be  subjected  to 
a  very  high  vacuum.  On  small  tubes,  especially,  it  is 
undesirable  to  use  the  special  glass,  as  a  lump  of  it  will 
usually  cause  the  tube  to  crack  on  cooling.  When  such 
glass  is  not  at  hand  or  is  not  to  be  used,  the  procedure 
is  altered  somewhat.  The  tail  which  is  drawn  out  is 
very  fine,  having  only  a  sufficient  diameter  so  that  when 
it  is  cut  off  the  wire  can  be  inserted  in  it.  Such  a  fine 
tail  is  readily  made  by  heating  a  small  spot  on  the  tube, 
touching  it  with  a  warm  platinum  wire,  removing  from 
the  flame  and  drawing  out  the  tail  with  the  wire.  After 
cutting  off  the  tail  the  wire  is  inserted  in  it,  being  held 
on  a  scrap  of  glass  as  in  the  previous  case,  and  the  wire 
and  tail  heated  until  the  latter  shrinks  back  into  line 
with  the  walls  of  the  tube.  If  too  great  shrinkage  occurs, 
the  place  may  be  blown  out  gently  after  reheating. 
Thus  the  wire  is  sealed  through  the  wall  of  the  tube  with- 
out changing  the  thickness  of  the  latter,  and  consequently 
without  developing  undue  stresses  at  that  point.  Such 


MODIFIED  METHODS  AND  SPECIAL  OPERATIONS    55 

a  joint  must  of  course  be  carefully  reheated  and  an- 
nealed. With  fine  platinum  wire  there  is  very  little 
risk  of  the  tube  cracking  if  care  is  taken  to  avoid  forma- 
tion of  any  lump  and  to  reheat  the  whole  circumference 
of  the  tube  at  that  point. 

Any  glass  adhering  to  the  end  of  the  platinum  wire, 
where  the  scrap  of  glass  was  sealed  on  for  a  handle,  may 
be  removed  when  the  glass  has  cooled  by  crushing  it 
carefully  with  a  pair  of  pliers. 

SEALING  VACUUM  TUBES 

Tubes  which  have  been  evacuated  usually  are  sealed 
off  while  they  are  still  connected  to  the  vacuum  pump. 
The  connection  should  be  through  a  small,  rather 
thick- walled  tube.  When  this  is  to  be  sealed,  it  is  slowly 
heated  toward  the  softening  point.  As  the  glass  just 
begins  to  soften,  the  air-pressure  will  force  it  in,  and 
care  must  be  taken  that  the  softening  is  uniform  over 
the  whole  circumference  of  the  tube.  As  the  shrinking 
goes  on,  the  tube  is  gently  drawn  out  to  make  a  thick- 
walled  cone  at  that  place,  and  the  end  is  drawn  off  as 
soon  as  the  tube  is  sealed.  The  principal  point  to  be 
guarded  is  the  thickness  of  the  walls  of  the  cone,  and 
uniform  heating.  A  thin  place  or  a  hot  place  will  give 
way  under  the  air-pressure  and  be  sucked  into  the  tube. 

CLOSED  TUBES  FOR  HEATING  UNDER  PRESSURE 

(Carius  method  for  determination  of  the  halogens  and 
sulphur.)  In  this  case  the  tubing  used  must  have  thick 
walls  (usually  about  3/32  inch)  to  withstand  the  pressure. 
Its  external  diameter  is  usually  about  3/4  inch.  One 
length  will  usually  make  two  tubes  of  standard  length 
for  the  cannon  furnace.  Especial  care  must  be  taken  in 
heating  and  cooling  it  on  account  of  the  thick  walls.  A 


56       LABORATORY  MANUAL  OF  GLASS-BLOWING 

length  is  gradually  warmed  in  the  center,  finally  heated 
at  that  point  until  soft,  drawn  out,  cut  apart  and  an- 
nealed. Taking  one  of  the  pieces,  the  cone  is  carefully 
heated  and  shrunk,  as  in  Exercise  4,  until  its  walls  are 
as  thick  as  those  of  the  main  tube.  A  flame  with  a  little 
tinge  of  yellow  should  be  used  for  this  operation  to  pre- 
vent devitrification  (page  2),  as  the  thick  glass  shrinks 
slowly.  The  tail  is  now  drawn  off  and  the  whole  end 
heated  and  gently  blown  several  times  to  make  a  rounded 
end,  like  a  test-tube,  with  walls  as  thick  as  those  of  the 
main  tube.  This  must  be  carefully  annealed.  It  is 
more  important  that  the  walls  be  thick  than  that  the  end 
be  nicely  rounded:  it  may  indeed  be  left  somewhat 
conical  in  shape. 

At  a  point  about  two  inches  from  the  open  end  of  the 
tube,  it  is  slowly  warmed  and  finally  heated  to  the 
softening  point.  Grasping  the  open  end  with  a  pair  of 
crucible  tongs,  it  is  cautiously  pulled  out,  a  little  at  a 
time,  usually  during  rotation  in  the  flame,  to  make  a 
constriction  of  moderate  wall-thickness,  'but  of  sufficient 
internal  diameter  to  admit  the  tube  containing  the  sub- 
stance. After  annealing  this,  cooling  and  cleaning  the 
tube,  the  acid  and  salt  are  introduced  (the  former  by 
means  of  a  long-stemmed  funnel)  and  the  tube  is  in- 
clined and  rotated  about  its  axis  so  that  the  acid  wets 
its  surface  about  half  way  up  from  the  bottom.  The 
substance  is  now  weighed  out  in  a  piece  of  thin-walled 
glass  tubing,  closed  at  one  end,  and  about  two  inches  long. 
Inclining  the  large  tube  at  a  suitable  angle,  the  small  one 
is  introduced,  closed  end  first,  and  allowed  to  slide  down 
the  walls  of  the  large  tube  until  it  reaches  the  place  where 
the  acid  has  wet  the  tube.  Here  it  will  stop,  and  if  the 
tube  is  kept  inclined  during  the  rest  of  the  operation  it 
will  roll  around  inside  the  tube  at  this  point  and  thus 
not  get  down  where  any  acid  is  likely  to  get  into  it  and 


MODIFIED  METHODS  AND  SPECIAL  OPERATIONS    57 

produce  any  pressure  by  decomposing  it  before  the  open 
end  of  the  tube  is  sealed.  Now  the  tube  is  held  in  an 
inclined  position,  taking  care  that  the  acid  does  not  reach 
up  to  the  substance,  the  constricted  portion  cautiously 
warmed  and  shrunk.  It  is  finally  shrunk  and  drawn  out 
into  a  somewhat  elongated  cone,  with  walls  as  thick  as 
the  rest  of  the  tube,  and  when  this  is  accomplished  the 
end  of  the  cone  is  sealed  and  the  waste  piece  drawn  off. 
Anneal  with  great  care,  and  cool  in  such  a  position  that 
the  acid  cannot  reach  the  hot  glass.  The  shrinking  of 
this  cone  takes  a  good  deal  of  patience,  and  is  one  of  the 
most  important  parts  of  the  process.  If  the  walls  are 
left  too  thin,  the  tube  may  burst  when  heated,  and  the 
whole  labor  is  lost.  If  care  is  taken,  the  same  tube  can 
be  used  for  a  number  of  determinations,  until  it  becomes 
quite  short. 


INDEX 


Annealing  glass,  4,  24 

Bellows,  4 
Bending  glass,  8 
Blowing  glass,  13,  19,  20,  21,  24, 
29,  31 

with  a  rubber  tube,  22 
Blowpipe,  4 
Bulb  at  end  of  tube,  28 

in  middle  of  tube,  32 

very  large,  32 
Bulbs,  string  of,  33 

Capillary  tube,  drawing  on 
larger  tube,  9,  54 
tubing,  working,  43 
Carius  method,  tubes  for,  55 
Closed  circuits  of  tubing,  48 


Glass,  bending,  8 

blowing,  13,  19,  20,  21,  24, 

29,  31 
collecting  for  bulb,  29,  31, 

32 

cutting,  7 
defects,  2 
grinding,  47 
hard,  1 
knife,  7 
lead,  1 

qualities  desired,  1 
rod  and  tube,  joining,  45 
rod,  working,  44 
shrinking,  18,  19,  22,  26 
soft,  1 
working     temperature,     1, 

13,  19,  27 


tubes,    for    heating    under       Grinding  stopcock  or  joint,  47 

pressure,  55  Ground  joints,  51 

Collecting  glass  for  bulb,  29,  31, 
32 


Constricting  a  tube,  10 


Handle  on  stopcock,  mending, 
45 


Crystallization     of    glass,     see      Hard  glass,  1 


Devitrification. 
Cutting  glass,  7,  25 

Devitrification,  1,  2 
Drawing  out  a  tube,  9,  18,  19, 
27 

Flanging  a  tube,  11,  14 
tool,  11 

Gas-washing  tube,  35 
Glass,  annealing,  4,  24 


Holding  tube,  13,  14 

Insertion  of  tube  through  an- 
other, see  Sealing  a 
tube  through  another 
tube. 

Joints,  ground,  51 
Joining  rod  and  tube,  45 

tubing    end    to    end:  first 
method,  16 

second  method,  20 


59 


60 


Joining  tub'es'  of  cliff efent  cHam--1 

eters,  25 
a  new  tube  to  a  stopcock,  48 

Kjeldahl  trap,  41 

Lead  glass,  1 

Lump  of  glass,  removed,  18,  19, 
20,  21,  24,  26,  30,  38 

Platinum     wires,     sealed     into 

glass,  1,  52 

Position  for  glass-working,  5 
Pressure,     tubes     for     heating 

under,  55 

Quality  of  glass,  1 

Rod,  glass,  working,  44 
Rotation  of  the  tube,  13,  19 
Rounded  end  of  tube,  35,  38 
Rubber  tube  used  for  blowing, 

22 

Sealing    a     tube    through    an- 
other tube,  35,  39 


Sealing  vacuum  tubes,  55 
Shrinking  glass,  18,  19,  22,  26, 

31 

Side  tube,  blowing,  22,  25 
Soda  glass,  1 
Soft  glass,  1 
Spirals,  making,  50 
Stopcocks,  mending,  45 
Suction  pump,  39,  42 
Sulphur  dioxide  tube,  28 

"Tail"   of   glass,   drawing  out, 

9,54 

removed,  30,  35 
Tubes,  closed,  for  heating  under 

pressure,  55 
"Tee"  tube,  22 

on  capillary  tubing,  43 
small  side  tube  on  a  large 
tube,  24 

Vacuum  tubes,  sealing,  55 

Working  temperature  of  glass, 
1,  13,  19,  27 


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1EC   21  1943 

Ifc'x 

DEC  22  1943 

REC'D  ' 

L.O 

APR  J  5  1957 

UBRARY  USE — iigCTO 


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